why do you say this?
the 8800GTX/Ultra has had one of the longest lifespans for any piece of hardware that I can imagine
Not counting the 9800GX2 (because it's really an SLI card) - the 8800GTX, to date, is the most powerful graphics card you can buy for high resolution gaming (forget the Ultra, it's just an overclocked GTX). It holds well against all its new counterparts. For a card that was released in November 2006.. that's really quite an accomplishment I think. I can't recall any other card lasting this long, and consider that it will still be on top until the 4xxx and 99xx stuff come out
So I assume that when the 9900GTX comes out, if it's really that much of a leap in performance, it'll probably be a good investment that'll last (heck, if I don't have to change my graphics card in 2+ years knowing it'll always be on top, I don't mind spending $500+)