I know for a long time that people should NOT put more than 3.3V on the GPIO pins. They also give out 3.3V when high.
I did some research and it seems no one really bothered asking. Almost all of them talk about the maximum current.
If I am supplying the Pi with 5V, why are the GPIO pins not 5V tolerant?
Arduino pins more or less follow the input (or VCC) voltage. If it's a 5V model, the pins use 5V. If it's a 3.3V model, it uses 3.3V. Anything above those would more or less fry it.
I should probably ask Broadcom about this.