I think this is an innovative approach to getting more people involved with grid computing for major computations and a clever way to market it in general. However, I agree with some other people here, there has got to be some sort of licensing issue. As much as the whole "you clicked okay to the TOS, you gave us permission." is a tank in court, it still seems to risky. If nothing else, it would risk users no longer using the games from the providers using that service if they found out that their computer slowed down at all during playing that game because it was doing things it wasn't supposed to. Not that I would likely have a problem with it, but lets face it...the general public is slap happy with lawsuits.

Also privacy issues in the entire concept. I didn't notice any (note: I didn't go out of my way to find one either) way for the end users to directly go and see exactly what kind of materials were being processed and what data, if any, was being collected from the user's machine. That might also be a source of trouble in the long run.