Most Mac applications support something called Cocoa key bindings, a fancy term for system-wide keyboard shortcuts for navigating and working with text.
Some will probably be familiar to you, such as combining Cmd with the arrow keys to move the cursor within the current line or document (or Cmd-Shift plus an arrow key to select text). There’s also Option-Left Arrow and Option-Right Arrow, which move the cursor through your text word by word.
Others are less well known. Control-A, for example, moves the cursor to the beginning of the paragraph its in; Control-O splits the line the cursor is currently on, inserting a return without moving the cursor to the new line; Control-T transposes the two letters on either side of the cursor.
It’s worth noting that Lion has changed the behaviour of the Option-Left Arrow and Option-Right Arrow shortcuts. In Snow Leopard, pressing Option plus an arrow key treats certain punctuation-separated strings (like.this.one) as separate words. This means you can use the Option key and an arrow key to navigate between each of those three words. Lion, on the other hand, treats such strings as single words. Lion’s change may well make sense for you. But for other people – such as anyone who types (and edits) URLs a lot – that change may be less welcome.
Tweaking the Word Break setting in the Language & Text preference pane will make keyboard shortcuts in Lion behave more like they did in Snow Leopard
Fortunately, there’s a way to make Lion’s keyboard navigation behaviour match Snow Leopard’s. Launch System Preferences and open the Language & Text pane. On the Text tab, look at the Word Break option on the right. Lion’s default selection is Standard; to emulate Snow Leopard’s behaviour, change that to English (United States, Computer). This Word Break preference was introduced in Snow Leopard, but Lion changed the default to Standard).
Once you’ve changed the preference, you’ll need to restart any open apps to get them to take advantage of your new setting. Also note that certain programs including BBEdit (www.barebones.com) assert their own preferences for some key bindings, so making this change may not affect them. (However, you can make BBEdit adopt many – but not all – Cocoa key bindings by opening the Keyboard pane of its preferences and selecting Emulate Emacs Key Bindings.)