Happened to come across a pointer in Slashdot to a Wired article. From the article -
BERLIN -- A security researcher has a devised a novel attack on online anonymity systems in which he literally takes a computer's temperature over the Internet.
The attack uses a phenomenon called "clock skew" -- the tendency for the precise clocks in modern computers to drift off of the correct time at slightly different rates, which can be affected by heat.
As I understand it, the basic premise goes like this. It seems possible to identify a computer based on clock skew. Clock skew is unavoidable although most digital systems try their best to reduce it. You change the temperature, you change the clock skew. So overload a particular server suddenly and there is a change in its clock. This means the time stored on that server also changes. Now use timestamps to find the server which has drifted off. This is not the entire story, read more at Wired.
This is a rather roundabout way of doing things. Not really the best way to do it, but what it does show is that such things are possible. Perhaps this concept might be useful in some other context. Personally, I don't expect such attacks to come in anytime in the future. There are far simpler and effective ways and it doesn't make sense to use such a complicated method.