I love the fact you can now earn achievements on RetroPie.
If your interested it is very easy to do so.
You will need to make a account on http://retroachievements.org/
You will want to edit your settings in /opt/retropie/configs/all/retroarch.cfg
You will want to add these to your settings.
cheevos_username = yourusername cheevos_password = yourpassword cheevos_enable = true
Save and reboot your RetroPie. Enjoy