Perhaps you considered Mac OS X 10.7 Lion
While I appreciate a new version as much as the next tech guy, I wouldn't recommend anybody to update yet.
- it's slow - connecting to 127.0.0.1:8080 took me 62 seconds, mundane tasks like cmd-tabbing lags sometimes, etc. Something's off.
- exaggerated animations - due to their graphical intensity, they have perceptible rendering times... in a desktop UI. Does not go.
- extremely cumbersome to use without a trackpad - means you sit with the computer in your lap rather than plug in external keyboards etc.
- they inverted the scroll direction. What the hell, man. "Natural scrolling"? Sheer gimmick value.
- Launchpad... I'm not sure why you would prefer a modal interface that only allows dragging as mode of operation. Gimmick again.
- Mission Control seemed like a good idea but it turns out you can't rearrange spaces, nor rename them - so rather "Mission Happenstance" than Control (and don't get me started on the auto-rearrange feature)
- you can now scroll past the beginning and end of the content, and very few applications are designed for this leading to UIs looking goofy
- "Press and hold" disables keyboard repeat... for most keys. (The feature itself only works on Apples own layouts, with no document detailing how to implement this for your own keyboard layouts having been published.)
- Browser back/forward with three finger swipes no longer work, Apple decided to use them for Spaces - you have to use the keyboard or nav buttons, unless you happen to use Safari which now uses horizontal two-finger swipes
- refreshing new UI look
- fullscreen now integrates with Spaces
- umm... I guess the new UI is pretty neat, yeah