I have a B version Pi and just set up a new RetroPi. I grabbed the full image (this is remarkable, by the way) and booted it up.
1) I put some SNES roms on and ran into performance issues like everyone else. As the (very useful) thread suggested at 2.2 step by step guide I switched to pisnes for emulation. Originally, I tried commenting the first two commands – this gave me a black screen. Currently I just deleted the two and it now starts.
However, my issue is that the controller commands do not work. I tried both a straight copy from the thread as well as matching my settings that I got from /opt/retropie/emulators/RetroArch/installdir/bin/retroarch-joyconfig (these settings work for the ES menu and the out of the box SNES emulator). I am using a wireless Xbox 360 controller and the official dongle.
2) Should the out of the box GBA emulator work? None of my games run.
3) How can I enable a turbo button for a game (specifically Pokemon Blue on GB)?
As a side note, Cave Story seems to crash any time I load a saved game. I don’t care if this works for me or not, but I did want to note a symptom. Doom appears to run perfectly fine.