Mac OS X has been around for more than 10 years. You’d think that by now there wouldn’t be much room for improvement. But this latest version – 10.7 if you’re counting – would prove you wrong.

Apple says Lion adds 250 new features to OS X. Many are borrowed from iOS. Some are tailor-made for new Mac users. And others improve (or fix) features that have been around for a while. Do these changes make Lion a must-have for you?

To help you answer that question, we’ve assembled summaries of the most important new features, and Macworld’s Jason Snell has written an extensive review. Read on and decide for yourself.

Safari

The flagship feature of Safari 5.1 is Reading List, which lets you mark interesting articles for reading later. When you come across an article on the web that you just don’t have time to read there and then, or that you want to keep for reference, you choose Bookmarks > Add To Reading List (or press C-Shift-D).

You can view your reading list at any time – it appears as a sidebar on the left side of the Safari window – by choosing View > Show Reading List, by clicking the Reading List icon in Safari’s Bookmarks Bar, or by pressing C-Shift-L; click any article in the list to view it in the main part of the Safari window.

In some ways, Reading List is similar to services such as Instapaper and Read It Later. But Reading List lacks some features that make those services popular making it, in many ways, just a pretty list of bookmarks.

Swipe to navigate

Like the rest of Lion, Safari 5.1 now works with a number of touch-based gestures.

If you double-tap a block of text, for example, Safari will zoom in on that column or paragraph; double-tap again to zoom back out. You can also zoom by pinching in and out with your thumb and index finger. With a two-finger swipe, you can navigate backwards and forwards in the current tab’s history. Oddly, the entire page seems to slide off the screen, which makes it appear as though you’re switching between tabs. Unfortunately, there doesn’t seem to be a gesture for switching tabs.

Safari also adopts Lion’s full-screen mode. Click the full-screen button in the upper-right corner of the Safari window (or press C-Control-F), and the current Safari window stretches to fill the entire screen.

There are some nice improvements to Safari’s security. The new Private AutoFill feature won’t automatically enter your personal info into web forms until you give the OK; it even lets you choose the info to be filled. And, according to Apple, Safari 5.1 has better sandboxing – which ensures that websites and web applications don’t have access to data from any other site or application (or to data on your computer).

Mail

In Lion, Mail has received one of its most significant updates yet. For starters, it now has a widescreen display option, which displays its message-preview pane to the right of the message list – in fact, that’s now the default view.

The other big change is an improved conversation view. While Mail in Snow Leopard had Organize By Thread, that feature simply grouped all the messages in the current list with the same subject. Lion’s Mail gets it right: if you turn on the Show Related Messages option, all messages in a given thread – regardless of where those messages currently reside – are shown. You see the entire message thread, including your replies, in an easy-to-read list.

Is less more?

Mail’s interface also gets a Lion-like makeover, with new toolbar buttons, minimalist scroll bars, and, sadly, iTunes 10.5-like monochrome sidebar icons. There are also new inline buttons (below the header) for deleting, replying to, or forwarding a message. The header area itself has been simplified, showing just the sender or recipient, subject, and date; clicking Details gives you the traditional header view.

There’s also a Favorites Bar just below the traditional toolbar. Initially stocked with buttons for Inbox, Sent, Notes, Flagged, and Drafts, you can have it hold almost anything – mailboxes, folders, smart folders, and so on. Click any button to get to what you need. The Favorites Bar also enables some brand-new keyboard shortcuts: C-1 to C-9 are automatically assigned to viewing the first nine items in the Favorites Bar; add the Control key to any of those keyboard combinations, and selected messages are moved to the appropriate favourite mailbox or folder.

A wider view

As with other Lion apps, Mail can be used in full-screen mode. The main benefit is that it gets rid of on-screen clutter while you work with your email. Mail takes it a step further, however. When you open a message in its own window or you compose a new message, background Mail windows are dimmed to let you better focus on the message window.

In Snow Leopard, you had to set up email accounts within Mail, contacts-server accounts within Address Book, calendar accounts within iCal, chat accounts within iChat, and so on. In Lion, there’s a single Mail, Contacts & Calendar pane in System Preferences (clearly inspired by the one in iOS’ Settings app) where you can set up and configure Exchange, MobileMe, Gmail, Yahoo, and AOL accounts, as well as generic email, chat, CalDAV, CardDAV, LDAP, and Mac OS X Server accounts.

iCal

Apple’s calendar program gets some big changes in Lion. Many of the visual tweaks are borrowed from the Calendar iOS app on the iPad, with a focus on giving you more room to see appointments.

New look

The first thing you’ll notice is that the grey title bar has been replaced by a leather-like pattern that looks like an old desktop calendar.

The list of calendars, which in the past was a sidebar that you could either show or hide, is now hidden by default; it appears as a pop-up menu when you click the new Calendars button. You can hide groups of calendars in the list by clicking the word Hide, which appears when you hover the cursor over a heading. This doesn’t hide events from those calendars, just the list of calendars.

To the right of the Calendars button is a plus-sign (+) button. Click it and up pops a Create Quick Event window that lets you add events to your calendars by typing natural phrases. For example, type ‘Dinner at 10 Downing Street at 7pm on Saturday’ and iCal will create an event with the name ‘Dinner at 10 Downing Street’ from 7:00 to 8:00 on the next Saturday. Or change ‘at 7pm’ to ‘from 7pm to 9pm’ and ‘Saturday’ to ‘25 August’ to create an event that lasts two hours on that date.

Year at a glance

In addition to updated versions of the Day, Week, and Month views, there’s a new Year view that shows mini calendars for each of the 12 months; the current month and day are highlighted. This view uses colour coding to show how busy each day is, from white (little or no activity) to yellow, orange, and red (busy, busier, ridiculously busy).

A feature that’s missing is the ability to click a calendar in the Calendars list and create a new event in that calendar. Previously, picking a calendar and selecting File > New Event or double-clicking in iCal would create it on that selected calendar. Now, double-clicking creates the event on your default calendar, and you have to edit the event to select a different one. But clicking and holding on the Create Quick Event button brings up a pop-up that lets you choose a calendar.

Address Book

The new Address Book looks much like the Contacts app on the iPad. That’s not the only change. In Snow Leopard, Address Book either displayed three panes – Group, Name, and Card – or one card at a time. In Lion, those views have expanded: you can view a contacts list on the left and a selected card on the right, multiple lists on the left and contacts on the right, or (again) one card at a time.

Faces and names

Address Book can match faces you’ve identified in iPhoto to your contacts. Double-click the picture box on a card, and then click the Import Face From iPhoto button (the far-left button at the bottom), and you’ll see a grid showing faces associated with that name in iPhoto. Click on a picture you like, resize or pan it as you wish, and then choose it by clicking the Set button.

Recognising the importance of social networking, Apple has added two new fields to Address Book. Twitter and Profile. Profile gives you the option of entering a profile name for a Facebook, LinkedIn, Flickr, Myspace, or Twitter user.

iChat & FaceTime

One of the most significant changes in iChat is that you can now log in to Yahoo instant messaging accounts (in addition to AOL Instant Messenger [AIM], me.com and mac.com accounts, Google Talk, and Jabber).

iChat also allows you to combine separate accounts into a single, unified buddy-list window, and to set one status message for all accounts (see ‘10 little things’ overleaf).

Full-screen chatting

Another smaller but welcome upgrade is the ability to press C-F (or choose Edit > Find) and start typing a buddy’s name, and have iChat filter your buddy list and show only entries that match what you’ve typed.

Videoconferencing in iChat gets an update, too. You can leverage all of Photo Booth’s new effects while video chatting. Like other Lion applications, you can run iChat in full-screen mode – but only when you’re video chatting.

In Lion, FaceTime (Apple’s application for video chatting between Macs and iOS devices) also supports full-screen mode; as in iChat, full-screen calls get their own space.