Look at this:
(http://petersphotos.com/temp/dual%20ati.jpg)
I've got two GPUs. I have a single GPU task and a dual GPU task queued. Boinc chooses to run the single one on one GPU leaving the other idle. WHY?!?!? Why not download more?!?!?
Yes I know, it's BOINC and not BOINC tasks that's causing it (probably).