Personally I'll be doing the same thing as my good friend Inziladun
Vista on it's own is hardly worth the money at the moment, since there are no DX10 games out. There's only one DX10 graphics card out at the moment, and it costs silly money. I definitely won't be buying nVidia again anyway, after the serious crashing issues I've been plagued with on my current card (7950GT). Waiting until the next-gen ATI cards are released seems more prudent, in my book, and also until the manufacturers have fully got to grips with the new technology.
In 6-12 months time, we will see some decent DX10 titles, cheaper, better DX10 cards, and hopefully a bit of a fall in the price of upgrading to vista. Until then, I'll be holding onto my precious pennies.
Same as Inz said, anyone who has enough money to shell out nearly $1000 on a graphics card and operating system, knowing that it won't allow them to do anything they couldn't already, has more money than sense.