When I had problems with P7 on release, I put it aside and used P6, waiting for them to get a couple service releases in place. SR2 is what brought me into P7 a lot more fully. I mention this because I'm not sure that this is a P7 issue or an SR2 specific issue, Firefly Renders at high settings seems to be heating my CPU more than any other application (or game) I've used. Of course, having a dual core CPU, it's worse with 2 cores rendering than just one, but it's really amazing the heat load it can produce.

For me, the warm days were the tipping point, but I can easily imagine that some people using the stock coolers for their CPUs may be experiencing heating problems even in normal temps. and even if overheating has not been an issue for them in the past.

Cleaning out dust in the case is definitely a good thing to do routinely, it insulates heat a lot more than people realize. Thanks for mentioning it, because I haven't done mine recently. Time to buy some canned air :)