About a year ago I switched from Linux Mint to Ubuntu because I had gone to work for Zend and Zend did not support Mint.
I had been running Ubuntu 12.04 32 bit on a Thinkpad T61 and kept that version because Ubuntu 13.10 comes with Apache 2.4 which was not supported in Zend Server until version 6.3 (Feb 2014)
Having left Zend I though I would upgrade my Linux boxes to 13.10 and installed Ubuntu 13.10 64 bit on my Thinkpad 13.10.
Everything went as expected with the install but actually using Ubuntu 13.10 on my T61 was frustrating.
Ubuntu 13.10 64 bit began crashing a lot !
Click on the Unity Icon – CRASH (well, a bit more than 1/2 the time).
Open lots of Windows in Firefox, CRASH.
After a bit of searching I discovered that there seems to be a universal issue with the default (one source) drivers on Debian based distros and Nvidia graphics sets.
It turns out that Nvidia makes proprietary Linux drivers for their graphics sets as well.
Note: The hard core open source folks will tell you not to use closed source drivers and not to installed from unverified PPA sources.
In my case the steps below not only seems to ave stopped the crashing and increased my graphics performance.
Your mileage may vary.
sudo add-apt-repository ppa:xorg-edgers/ppa
sudo apt-get update
sudo apt-get install nvidia-current nvidia-settings
sudo apt-get remove --purge xserver-xorg-video-nouveau