Yeah, I have the sonic 2 betas aswell, they're quite interesting indeed (genocide city zone FTW).
Again, used to know a decent amount about game betas from my nerdier days, can't really remember much ATM though.
I do remember the glitch in the halo 3 beta that allowed you to easily get out and fly around valhalla. When the actuall game came out, me and a couple of mates tried very hard to get out of there, I remember we actually found a legal way of doing it in forge aswell, but it involved having about 8 people in one game helping with the very long glitch, so we gave up.