I got my gateway 2 days ago and played LOZ ocarina of time through the night (stopped at 9am) and right when saving, when pressing x on the homescreen everything froze. I turn it off and on and find out my save is corrupted. Felt like shit this entire day . I just might use beta 2 to avoid bad saves.
It's a tough choice: go with b1 to avoid bricking but randomly lose your save games or go with b2 but face a rare but possible brick. Either case kind of makes you want to just put the 3ds away until a new firmware is released. I think if you don't need emunand and are not playing recent games, then 1.2 is suppose to be pretty stable.