Overheating or running hot?
Yes, they run hot but the fan kicks on and should keep it useable. If you do have some tasks that use the 9400, it'll get hot but shouldn't overheat.
I classify overheating as massive frame drops, spinning beachball, cursor unresponsive or laggy and eventually a shutdown.
I've ripped via HandBrake a few dozen movies and mine never overheated though reaching into the 80ºC's for long periods of time. The Rev.A did throttle a little more than I would have liked but they both worked without shutting down.
I like the MBA's screen much better than the MBP's as well as the silver bezel.
My only dislikes would really be the non-upgradable RAM and the funky 1.8" drive. A SD cardslot would be nice in lieu of an additional USB port, more SSD space & RAM are necessities. Some more battery juice would be nice too.
I call it overheating because the throttling back has caused an otherwise capable 9400M to stall the flash video playback, especially on a large external display. The 2.26Ghz 13" MBP, with the same integrated 9400M and a comparable processor as a 2.13 MBA, has little trouble playing Hulu video externally while the MBA goes into an instant frame drop when I connect it to a 1920x1200 display.
I have no doubt that the MBA, either Rev. B or C, makes a great ultra-portable and secondary machine. My contention is simply that, while its technical specs are amazingly capable, the MBA has some serious thermal management issues (perhaps intrinsic to its form factor) that it cannot be used as a primary mac, not if you hope to pair it with a large external display.