400 Watts is no big deal, most cheap cases come with a PSU that's 400 watts.
The 8800 is the only card announced so far, but soon ATi will announce their R600 series and when the cards hit the market it won't take long before there all kinds of various versions, the 8600, the 8300, the ones which take GDDR4 and therefore save on power, the dual GPU architectures, the quad-SLi support etc.. etc..
PC gaming is a big thing for me, so is having a fast computer, I from time to time do a lot of heavy mathematics on my computer. In about a year or so I plan to build a new killer computer to replace this one, till then I'm not so sure Vista's extra power required to run and new weird bugs it introduces are really worth the fact I can open apps much faster with searching the start bar and everything looks prettier is quite worth it.
However, when the OS has been running for 6 months or so, Microsoft has quashed all the major initial bugs that people will be giving them bad press to start off with, applications start seriously taking advantage of Vista’s new features, then I’ll probably jump on board with a new computer and all.