1. Quick Look
Easily the best feature of the reinvigorated Finder, Quick Look gives you a sneak peek at the contents of a file without you physically having to open it in an application. It works with any kind of file, but is most useful for documents, presentations and spreadsheets where the new thumbnail previews doesn't always give you much of a clue about their contents.
Quick Look functionality is buried deep into the OS, enabling you to take advantage of it in any of the Finder views (it finds its best expression in the Cover Flow view). It even works in some apps - you can look use it to look at attachments in Mail, for example, as well as backed up files in Time Machine.
Quick Look can even handle multi-page documents. Open a PDF in Quick Look and scroll bars appear on the right side of its translucent window, enabling you to peek at every page. Ditto for picture selections.
Best of all Quick Look is fast to access - while you can mouse click over the icon in a Finder window, it's much speedier just to tap the Spacebar.
2. Time Machine
Leopard's killer feature is an automated backup program. It's aimed at people who know they should back up their precious files but either don't know how to; or are simply put off by the intimidating nature of most backup programs. The exception to this rule on the Mac is SuperDuper, which manages to balance simplicity with power.
Briefly, Time Machine backs up everything on your Mac when you first switch it on (a big 'on' switch is exactly all it takes). Then it makes incremental backups every hour, every day and every week until your backup drive is full. Backup drives can either be external FireWire 400, FireWire 800 and USB HDDs, or spare internal drives - the Mac Pro can hold up to four.
Apple has deliberately limited your customisation options to keep Time Machine simple. You can prevent certain files, folders or even disks from being backed up by selecting the Options tab in System Preferences > Time Machine. You can also set it to warn you when old backups are deleted. So far, so good.
Time Machine proves its worth when you want to resurrect a file you've accidentally deleted. To do that you simply click on the Time Machine icon in the Dock.
The application then magically glides into view, complete with geeky moving starfield and 3D view of previous Finder views stretching back in history to the time of your first full backup. You'll also see time represented as a series of marks - like on a ruler - running up the right side of the screen.
Right, remember that file you deleted? To find the last version you can either simply go back through time until you find it, or search for it using Spotlight, Apple's desktop search tool. When you do find the file, simply select it and then press the Spacebar to get a Quick Look view. To bring it back to the present, simply click on Restore and you're done.
File backup and restoration is rarely fun. In Mac OS X 10.5 Leopard it's an absolute treat.
Virtual desktops are nothing new on either on the Mac or PC. The basic idea is that you can set up multiple desktops - up to 16, but four by default - that enables you to free up precious disk space. You can keep Mail and Safari in one space, for example, iPhoto in another, iTunes in a third and games in a fourth. Sounds confusing? In Leopard it's very practical.