leopard
So I stayed up entirely too late playing with Mac OS 10.5 (Leopard).

The only thing I don't like is the removal of input managers from safari.

I like (in rough order)

1) Spaces. OMFG a virtual desktop system that isn't a usability nightmare! Seriously, I don't know how I lived without multiple desktops for so long.

2) Cover Flow View/Quicklook. This is pretty cool, especially since it's integrated into the mail client and is easily accessible in Finder. I have folders with hundreds of videos and pictures, and it's nice to be able to find that specific simpsons or friends episode. I kinda wish I had this at work, would make sorting through the millions of pages of documentation a little easier.

3) Safari 3. This isn't specific to leopard, but it's still pretty awesome. It feels a lot faster, and the in-page search is very nice.

4) Finder sidebar. Just like itunes. Makes my life simpler.
5) Dock stacks. Saves me a few seconds when launching an app or finding a file I downloaded a while ago.
6) Movies widget. Very nice for impulse movie watching.

I'm also looking forward to writing some dtrace scripts for monitoring, between that and the new dashcode interface, I could make a pretty sweet and comprehensive dashboard status widget.

Time machine is pretty cool too, I set it up on my external drive, and let it do its thing.

I'm trying the new mail app too, and it's pretty nice...integrates with rss feeds, picked up my gmail info pretty easily, has quicklook for attachments, spotlight search, etc, etc.