Was debating it, til I read all of the horror stories of using the latest Nvidia drivers in 64-bit. Constant crashes, still lacking basic features, and performance problems (major in some games).
I haven't had any crashes since starting on the 15x.xx line, I only use official WHQL drivers, currently on 162.22 with my 7900 gt.
Features I'm not so sure about, I don't use any features in the control panel, so wouldn't notice any missing ones.
Comparably, I'm not sure about performance either, as I haven't been gaming much at all in the past year. I can't complain about performance in the games I have played recently (ut2k4, Far Cry, civ4), but none of them push modern cards much anyway.
Major performance problems with WoW FWIW, it's been a documented problem in the release notes for a while now, non-issue for me, as I'm never going to play WoW.

edit: NVidia's release notes are actually quite good, worth perusing for anyone wondering if a certain feature is missing from a driver set, or if your favourite game has a known problem.