At this point in time the 9800GTX does certainly look like a good deal as long as you do not get "buyer's remorse" after the 4xxx comes out.
If it is going to be a vast improvement over what you currently have then go ahead and buy it. If the performance increase is marginal, then just wait until the 4xxx series is out to determine which card is best for you.
Well, I would be upgrading my whole system from an AMD 4400+ X2, 2GB Ram, X1900XTX 512 to an E8400, 4Gb, 2x 9800GTX SLI. At least that's what I was thinking.
Such difficult decisions!