Question: Is it possible to reliably run a Pi in an airtight (watertight) case or is some form of ventilation required for cooling? I'm assuming it doesn't chuck out too much heat, but am wondering whether running it indefinitely this way may cause issues.

Answer: 
There are **no ventilation or cooling requirements.**

This has been verified by an RPi admin [here](http://www.raspberrypi.org/phpBB3/viewtopic.php?f=2&t=1701).
Based on my test Raspberry Pi runs relatively cool even when the CPU is 100% loaded for longer periods, so I think there shouldn't be a problem (I did not try loading the GPU though).