Nvidia drivers do fail quite regularly, especially on laptops. Brightness control randomly stops working, suspend/resume is extremely unreliable, there are login issues on systems with both Intel and Nvidia graphics (supposedly solved with Mesa 12, which can only be found on Arch and Gentoo right now.) It's certainly not a panacea.

In my experience, the open-source radeon drivers are significantly more stable. Fglrx was a stinking pile of crap that has officially been abandoned - the whole driver team has switched to the open-source drivers, now.