Interestingly I still hold a fondness for Mac OS 9.2. If only I had today's apps on it. Snappy, fast, minus all the bling bling. Pity my old iBook's too old

That aside, Leopard was worthwhile for me. First and foremost, I need it for work purposes, and as an Cocoa Developer and Web developer, the development tools and command line tools update was worth it for me. I used to have to compile Apache2 by hand, it's now finally bundled with Apache2. Xcode 3 and Interface Builder 3 totally made some of my source code files completely redundant and sped up my dev time like mad.

And not to mention iChat with screensharing made collaborative work and troubleshooting easier. Had to help my other half with some Cocoa bindings, no way I can explain over IM, so screen-shared to show him step by step, and the next day, I had some php custom compile errors, he screenshared with me and fixed the problem - on top of that, the screensharing (which is basically remote desktop connection/vnc) also carries voice conferencing. So imagine while he was fixing the error, I can see everything he does on it and at the same time hear his explanations, which is really a nice touch.

Second was Spaces. I use a 12" PowerBook G4, screen real estate is sparse for me. I used to use DesktopManager (of which VirtueDesktops was later based on), but it had quirks that made the whole experience not very pleasant.

Third was the data detectors in Mail.app. I get a lot of events and seminar invitations, so it makes things easier for me to add them to my iCal.

But that being said, if you have nothing in particular to look forward to - if you're just a general user, you may not feel it as much. It would be fun for the first few discovery days/weeks, but after that, it's just another OS, unless there are things you're specifically looking forward for which is a major improvement.