[kaido]

In the past couple days I've had a few random shutdowns, which I suspect can be attributed to overheating. Right now I'm basically in a one-room studio and since I don't have a lot of room, I sometimes use my MacBook on my bed, just on top of the sheets (not the comforter). Yesterday I had two random shutdowns while using it on the bed. It's not really sunk into the bed or anything, but I think the sheet cloth may have some kind of negative effect on the vents or cooling system or something. The rear middle bottom was extremely hot (under the word "MacBook" on the screen, but on the bottom a few inches in). I've upgraded the MacBook with 2 gigs of ram and a 7200rpm hard drive, but the areas where both of those are installed are as cool as room temperature.

Yesterday it took the MacBook awhile to restart and today I was able to start it right back up again. I propped it up on a small notebook and after starting up, the fans kicked into high-gear. I've had this machine for about a month or so and it's been flawless. I'm pretty sure the problem is related to having it sit on cloth and then overheat; has anyone else experience a similar issue? It simple shuts down. Just "blip" and a black screen.

[imitchellg5]

That could be a heat issue, I would take it in to Apple.

[HouseSold]

Yesterday it took the MacBook awhile to restart and today I was able to start it right back up again. I propped it up on a small notebook and after starting up, the fans kicked into high-gear. I've had this machine for about a month or so and it's been flawless. I'm pretty sure the problem is related to having it sit on cloth and then overheat; has anyone else experience a similar issue? It simple shuts down. Just "blip" and a black screen.

You won't know for certain unless you monitor your temps with a utility, such as core duo.
You might reset your PMU. (remove battery after shutdown, hold power button down for 10 seconds and restart)
Even perform PRAM reset (simultaneously press Cmd option P-R after pressing power from shutdown state)
These have become Apple's own 'most recommended by phone staff' suggestions.
Document all of this, temp and performance wise, for your own recollection later.

Study the underneath of your MacBook, just for understanding; the essential cooling is the narrow slot running across below the display which works by convection. When the operating temps cause the heat sensor to activate the fans, it is usually warmer than convection can handle alone. Most of the underside of the MacBook cooling is just radiating a little heat from the case material itself, especially below the centrally situated central processor heat sink and the power supply circuitry (magsafe connector) side.
We use the coolpads ( www.coolpad.com ) at home and office successfully for that little air gap that resting on a bed or blanket or even on your lap wearing clothing of course, may not provide. Others have mentioned a cutting board used as a surface insulator.
Let us know how it goes.
YMMV.

[kikkoman]

the system log should contain entries for forced shutdowns due to overheating