I really like Leopard, but it lacks that one sledgehammer feature that insists you immediately make this the first day of the rest of your Leopard life. Instead, Leopard is a game of inches. It doesn’t have one or two major features that’ll convince you to upgrade, but rather a half dozen or more minor ones. And the half dozen features that convince you will be different from those that convince me.

Feature by feature So should you upgrade? To answer that, try to picture Leopard as a collection of standalone programs, figure out how much you’d pay for the ones you want on their own, and then do the math. Here’s my own appraisal.

Time Machine Leopard’s built-in backup tool is definitely cool, even if I can’t think of the last time I actually needed its “infinite undo’ backup scheme. For my needs, Shirt Pocket’s SuperDuper (www.shirt-pocket.com), which makes a complete bootable backup of my drive once a week and syncs my key files with my iPod every evening, is still a better alternative. I’d pay £15 for it.

Spaces I love it: it’s clean, it’s simple, and it works fantastically. I tend to create a new Space for every program that works best in full-screen mode, like iMovie, InDesign, or Aperture. Still, it’s hard to get people to cough up more than £19 for a one-trick pony.

Back to My Mac Apple has finally done something ambitious with .Mac: Pop open your MacBook in a hotel room and – glory be! – your desktop iMac appears in the Finder. So hell, yeah: I’d pay real money for this – say, £99 – if it were a shrink-wrapped DVD at an Apple Store.

Mail It’s truly a whole new program in Leopard, one that finally understands that a single message can represent a new contact, an appointment, a new item on the to-do list, and a note to yourself. Bundled together, Mail, iCal, and Address Book could legitimately become a new £49 iPackage.

iChat Like Mail, iChat has moved to the next level. With its ability to run presentations and its support for live screen sharing and chat recording, it has also suddenly become something that’d cause people to reach for their wallets and pull out £39.

The Finder Apple apparently thinks it perfected its file manager in System 1.02, because we haven’t seen a truly fresh take on it in more than 20 years. But we have seen steady evolution, and that trend continues in Leopard. The Sidebar, for example, makes more sense now than it ever did, organising volume and directory resources in a way that you can ‘get’ immediately. I scoffed, sneered, and snickered at the idea of Cover Flow in the Finder. But I have to admit it: I was wrong. Cover Flow is perfect when I need to find a stray image in a gigantic folder full of junk, and I have a lot of those on my Mac. And if I need a closer view, Quick Look lets me eyeball that picture in full-screen mode without having to drag it into Preview or something. So although my mouth goes a little dry when the subject of ‘a more iTunes-like Finder’ comes up, I now have nothing but kind things to say as I pay my £39.

All that said, let it be noted that the new translucent menu bar option is a colossal-sized Box-O-Suck. And look! There’s a free prize inside: a travel-size Tube-O-Fail. It’s ugly and makes a critical part of the interface harder to see and use.

Spotlight What happened to the system-search tool is what should happen to every major new feature after its debut. The Spotlight team clearly listened to users. Search results appear in a Finder window. Search language is now more Google-like. You can do compound searches, as well as calculations and other search-fu. This version is also a lot faster than its predecessor. The new edition is clearly something for which you’d pay cash money – let’s say about £29.

Adding it up All told, just these new Leopard features would have cost me nearly £300 (£311, if you throw in £11 for that way-cool 3D holographic nebula on the box cover). And remember, there are dozens of features I haven’t even mentioned here.

No matter how you work the numbers, though, it’s pretty clear that Apple has yet again crammed way more than £85 worth of value into its latest OS update. It’s the magic number: just low enough so that most people will regard it as a reasonable expense without needing to resort to a lot of operatic hand-wringing over the decision.

See? It’s much simpler when you do the math.