I have to agree with eternal_fantasy because I've seen a similar variation in GPU usage even on the same work unit after starting up BOINC after a gaming session. I'll play with it some more and post back with any conclusive findings.

On another note, does XP or Linux give better performance with Fermi cards? I plan on creating a dual-boot with Win 7 for gaming and all other PC tasks and switch back to XP for better folding performance.