Its not really worth it right away, many companies wont have drivers out for hardware. It will have flaws. Its worth it for those who have Crysis preordered and have their DXX cards already.
It comes out January 30
And now that ive read about Readyboost, Readydrive, Sleep and you missed Superfetch, I think its just about worth it. This talks about these things: http://www.microsoft.com/windowsvista/features/foreveryone/performance.mspx The only reason im getting vista is because i need a copy of winxp and i can get an easy upgrade for cheaper than if i just bought vista. Now im happier that im getting it.
After reading more into the specs and such of Vista, I'm not sure I want it so much, considering the need for the faster and more expensive hardware, and the possibility for instability of software on the computer.