Fionn2003 :
The new chips are not even out yet, they will be at a premium for multiple months and either be near the same performance, or just barely over so its not really that big of a deal breaker for me.
I don't have any complaints about the capability of card you got, only that it will be surpassed by the GTX280 (definitely) and equaled by the GTX260 (probably) without SLI scaling issues in a few weeks.
My only criticisms of Nvidia regarding the 9800gx2 is that they should have done dual GPU on one PCB like ATI's 3870x2. Sometimes, they react to ATI and aren't as forward thinking as they should be.
Regarding launches, ATI actually had the 3850 and 3870 available at a reasonable price within a few weeks of the launch and Nvidia's done well with availability too; though it's hard to get the new card at exactly the MSRP right away.
I've never done true Crossfire or SLI. When I got that 7600gs, it was as a stopgap for an Nvidia 405 chipset barebones (replaced the PSU though) while I was waiting to see how the 8800 and 2900 cards would do. Turns out neither the X2900XT or the 8800gtx 320 were that great in DX10, so I just waited, but switched out for a PCIe x16 budget ATI board when I got the 3870x2.
With that card, I really liked the idea of internal hassle free Crossfire. Either card should be viable for another year or two, especially since AMD and Nvidia are improving their drivers to support internal Crossfire and SLI.
A single 4870 won't be any faster than my card, so I wouldn't think of upgrading right away now; it's just that any single GPU that equals a dual card or dual GPU card is a better solution with no scaling issues. The difference in our situations is that a single GTX280 will be faster than your card.
When to upgrade is subjective, but if you had to make that choice, the card's a good one. IMHO, dual GPU cards are one step towards dual core GPU's.