Funny. I spent a summer in 2009 in Vietnam, working on one of those old unbeatable Powerbook silver models, in an apartment without air conditioning. The fan would run at full power constantly, and finally gave up the ghost. There was no way to repair it where I was. So what I used to do was keep a bunch of Wired Magazines in the freezer, and put them under the laptop, changing them out every 20 minutes or so. The machine still works... but yeah, that fan noise is really a great subconscious reminder that you're using it too hard. Also a good way to know if your code just entered an infinite loop, long before any other warning comes up... and occasionally that clue gives you enough time to cancel a process before the input freezes.

[edit] Just had a cool idea, since this discussion is heading towards how subtly useful auditory cues have been in our workflow. What if different processes played fans at different pitches, so the total volume still added up? That could actually be really useful out-of-band state information.