Hmm, lots of anecdotes and complaining here. I've experienced no issues of the sort. Running perfectly smoothly here on 12.04, 64-bit. And I'm on a 4-year-old Pentium Dual Core machine, of all things.
On a side note, I gave up nVidia hardware altogether (about 4 years ago) because of endless issues with Linux (and macs). This thread isn't encouraging.