Tests performed by PC Authority found a Core i7 MacBook Pro to be running very hot, climbing to over 100 degrees Celsius.
The magazine had a Core i7-620M based 17" MacBook Pro on their hands for testing. While putting it through their benchmark suite, they noticed that it scored lower in Photoshop tasks then expected. Suspicious that heat might be affecting their results, they propped the machine on its side and repeated the test. Performance improved.
Having booted into Windows via Boot Camp, the group ran a Dwarf Fortress test that, according to PC Authority, got the temperature up to 84ºC. They said that the bottom casing was "almost too hot to touch." When running Cinebench 11.5, the temperature climbed to 90ºC and eventually broke 100 (101ºC specifically) during a second test of Cinebench 11.5 the following day.
The magazine argues that a flaw in the machine's cooling design caused the problem. The Fujitsu LifeBook SH760, which uses the same CPU, reportedly gets no hotter than 81ºC during the Cinebench test. Note that the SH760 uses a copper heat sink that vents out of chassis, unlike the MacBook Pro.
We've not done any testing of our own, nor have we heard of this issue before. I can tell you that my 2 GHz Intel Core Duo 15" MacBook Pro gets pretty hot during World of Warcraft marathons, but that was a known issue with that older machine.
If you've got one of the 17" i7 MacBook Pros, share your anecdotal experience with heating issues below.