I'm gonna point out that if you buy a pair of 8800GTS(G92)s you have effectively as good a pair of cards as if you bought 9800GTXs, can *still* use the "Step-up" program if you really think you need to, *and* spent less money if you decide you don't need to step-up after all.
This is coming from someone who has a 9800GTX and wishes he'd waited or gone with the 8800GTS in case the 9900s don't come out in time to use the step-up. My plan was to use the 9800GTX until the 9900s come out, then step-up the GTX while buying a 9900 for SLI...we'll see though.
Worst-case scenario with the 8800GTS, the 9900s are delayed, you don't get to "step-up," and you're stuck with two really good cards.
Keep in mind the 9800GX2 is not terribly impressive by any standards except the amount of heat it dumps into the case and the price tag.