I seem to be seeing a slow memory leak in the nvidia drivers, as far back as some of the 169's iirc. I've been running KDE 4.1 and svn-trunk for a while now, and have noticed X continually eats up more and more memory, and won't free any of it till X is fully restarted. I end up with X using 800MB+ Virt, and 300-400MB RES ram, and restarting KDE didn't help, I had to CTRL+ALT+BS or use the kdm restart script to get the memory back (even though no X apps besides kdm were running, X wouldn't free most of its used ram).
I've attached a compressed nvidia bug log if it helps any (generated after running for a little while, after restarting X)
edit: if theres a better way to help diagnose it, running extra programs, let me know
edit2: forgot to mention, I'm currently running the 177.70 drivers and seen the same thing with the 67 and 68 drivers.