The first time I experienced the 100% CPU bug was with an NVidia card (GeForce GT 330M). When I started mining I tried that and other NVidia cards (including a 9800 GX2 and 8800 GT).
Things were mostly fine when I switched to ATI cards. Two 5830s and a 5750. Catalyst 11.6 drivers, 0% CPU.

When I finally upgraded to Catalyst 11.8, then every single system hit 100% CPU. Setting the priority to "Below Normal" prevents it from slowing things down, but my CPUs still generates heat when at 100% load, 24/7.

I use GUIMiner, and it doesn't recognize my ATI cards when I use older drivers and SDK.