Just after reading this, a friend asked me to look at some funny behavior on his machine (Thinkpad T-series, I beleive)

I don't think it was related to the actual problem, but I also noticed that his CPU usage was unusually high. Checked and it was only when FF was running, but he wasn't running nay of the suspected add-ons.

The only thing there was google toolbar. I removed it and the CPU usage was down. Downloaded it again from google and reinstalled and no bump in usage.

It may have been because I chose not to enable page ranking and I have no idea if he had it enabled before, or it may have been a new revision of the toolbar software, but maybe that'll be a clue for someone else.