Dedoimedo posted a short tutorial explaining how to work around the problem of high CPU usage and slow system responsiveness in Ubuntu 12.04 Precise Pangolin with Nvidia graphics card

All right, the symptoms you're suffering from are the following: You've recently installed Ubuntu 12.04 Precise Pangolin and the proprietary Nvidia drivers for your card from the official repositories. Since, you've noticed sluggish behavior, slow windows switching response, high spikes of CPU when doing even basic things, CPU going up to 50% when opening the Dash, and other things that sour your mood.

Worry not. Dedoimedo will solve all your woes. Just as I solved your initrd issues, your Nvidia activation thingie in Natty, your Realtek problems in Kubuntu, we're gonna tackle this one with simplicity and elegance. So please follow me and enjoy another lesson in statistical engineering applied to resolving home problems.

  Ubuntu 12.04 + Nvidia - Heavy CPU usage