I've just aquired an Inno3D Geforce 8800GT (the non-OC version) and tested it with the beta driver.
It seems stable for now, but performance is quite bad.
I've upgraded from a 7600GT and the games I've tested so far run at the same speed (lotro, nfsmw, nfs carbon) or worse (oblivion) with the 8800GT.
Framerates are quite bad (this is to say that the 7600GT isn't giving outstanding performance) - in the 10-40 fps range in the titles mentioned.
(In situations like this I'd normally say that the bottleneck is somewhere else - cpu/ram/io, but I'm running on an AMD X2 5200+, 4gigs of ddr2-800 SPD 4-4-4-12 ram and raid-1 of two 500GB drives).
I didn't intend this to be a bugreport, I'm waiting for the stable release. If the issue still exists there, then I'll make some loud noises accompanied with lots of data.