not at the current prices of the x800 (around 500, 450 at cheapest), although when the prices do decrease later on (less than 400?) it's probably a fine investment, as these cards are a substantially dramatic improvement over the 9800s
i've got a 9800pro and i don't think i'll be upgrading anytime soon - it plays every game i have at max details fairly well. a tiny bit of a prob with "Far Cry" but ut2004, D-Ex 2, BF Vietnam, X2 - they all run fine fps > 50 (with high load).
at least wait till Nvidia bring out their latest and see if it measures up.
I've got tonnes of memory, an AMD fx-53 processor and a 5900 Ultra and I can still bring the system to it's knees! The games are still ahead of the hardware. There are DX9 features that aren't even used on DX9 cards because it slows them down too much.
The new cards kick bottom but are just OTT in price at the mo. If you've got the dough though....