I would wait, but I'm building my rig now, and don't have a PCIe card to hold me over...so I need something.
Also, I plan on dual booting Vista/XP so I can still play games in XP since performance is just not up to par yet in Vista(which I'm currently running).
On top of that, I have heard too much bad thigns about Nvidea and drivers with Vista so far that I would rather wait until maybe even the second round of DX10 cards before jumping in.