Don't mix the two. Apple has now confirmed there is a problem with the isight on the firewire bus, it will corrupt data going to or from the hard drive during periods of high disk I/O. This occurs whether or not you are using the camera, just so long as the camera is connected.

http://docs.info.apple.com/article.html?artnum=93498

Apparently the hardware gives preference to video over data (huuh?) so if the firewire bus is swamped, it tanks your data rather than making your video jumpy. I don't think this is the best way to handle it, I'd prefer jumpy video over corrupt hard drives but owell that's what we get.

This does not affect the macbook and macbook pro cameras because they are USB. I have not seen this issue with the isight imacs but they are firewire cameras so it would not surprise me if they were also affected, though I'd think by now we would have noticed the problem with them. (unless in their case they do not impact the bus if the camera is not in use?)

The link actually doesn't come right out and say it, but data going to/from the hard drive loses the fight and you WILL get i/o errors.