Dad and I both have the 2.16GHz version of the Macbook Pro. It gets really hot, both on the bottom and on the top above the function keys. The fans never seem to kick on noticeably, but I've heard of a "jet engine mode" that they can go into occasionally. It would be nice to knock the fan speed up just a little to cool off the Macbook, so it'll be comfortable while on a lap. Alternatively, perhaps there's some sort of add-on I could use, like adhering a custom-fit rubber mat to the bottom side to shield flesh from the heat dissipated by the aluminum case. If you have any ideas, let me know.

UPDATE: follow-up post.