Regarding SilverWolfs experience with heat issues on the M680:
Soon after getting my M680 (2.0 GHz CPU, 1 GB RAM) I noticed a lot of heat in the left-palm area below the keyboard and the underside. I checked with the chc program and saw idle temps in the 55 range, and 60+ when watching DVD's and/or running Photoshop and Web browsing (I'm not a gamer).
I waited a week or so, and eventually the heat dropped significantly to below 50 idle, 52-53 DVD watching, and 55-56 when adding Photoshop and/or Web browsing. I've seen it spike up to 60 just once briefly.
A month later, the machine remains at these lower levels, so with the corroboration of your experience I would say there is something to your statement about a break-in period for the thermal compound.