I have it on my computer (got it delivered this morning from Apple.com). Overall, I think it's a modest improvement. I haven't gotten a chance to fully explore it yet, and I need to go out and buy an external harddrive to test Time Machine. I think Time Machine has the potential to be BY FAR the best part of this upgrade, if it truly works as advertised. I don't really like the new dock/menu bar, and I feel they put in too much drop shadow. A bit too dramatic, for me...looks a bit like Vista.

On the other hand, Spaces is really neat. I haven't played w/ the new iChat yet, but iCal and Mail are better. Also, it's nice that all apps from Apple now have a unified look.