Man, do I want it! I've never been one to update OS's quickly. I've got an old beige Mac that is still running 8.1 (that's a pre-OSX system for the uninitiated). When I got my Quicksilvers in 2002 I ran OS 9.2 for a couple of years because I didn't want to mess with OSX. Didn't use it until Jaguar. Then when Panther came out I waited a year before upgrading to that. Tiger I went to much faster, upgrading after only a few months after it came out because it had some cool features.
But Leopard I really want. All kinds of good things in it. The most important for me is the new Finder, which works much more like Mail or iTunes but I especially like the preview mode, Quick Look, in Finder. I bought a Finder replacement app, Path Finder, a while ago mainly because it had a good preview feature and the few times I've stopped using it and gone back to Finder I've quickly gone back to Path Finder because I really needed the preview feature. Works even better now that InDesign makes previews as well.
But my favorite feature is Back To My Mac. If you have a .mac account (and I do) you can connect to any other Mac of yours that is registered on .mac and use it like you were there. Which means while I'm at work I can open my home Mac and vise versa. There has been many a time I've left things at work I wanted to work on at home and forgot to take with me. Nothing for it but to wait until I get into work the next day. But with the new Leopard feature I can access the work Mac right from the Finder. You used to have to buy Apple Remote Desktop for that, a $500 program.
Time Machine looks great too. It saves a snapshot of your system and files every hour, but not the whole system only what is changed. Suppose you have a file you've been working on for days, at some point you realize you really want to go back to the version you had yesterday afternoon. You can flip through Time Machine until you find just that version of it and copy it back your hard drive.
And there are several other cool features, too. Preview will now let you combine several PDF's into one. Partition your hard drive without erasing it. Notes and To Do's in Mail look interesting. They have Dashcode, which is supposed to make designing Widgets easy, maybe I'll give that a try. Guest login so if I want to look up some porn without Darcy knowing it's all gone when that Guest account is gone :-) Or Private Browsing in Safari will do the same thing.
But my rule is to wait until at least 2 updates on a new OS for them to get some bugs out, but it's going to be hard. What does keep me in check is that there are several system enhancement apps I use that aren't fully Leopard compatible yet so I have to wait for them. Also, I just can't afford it right now which is what is really holding me in check.