If you're running 4.0.4, than you're running a custom rom already. You can experiment with apps that require root (setcpu, titanium backup, wifi key recovery) or try flashing a new rom. Make sure to do a nandroid backup first (reboot to recovery and select backup) and wipe data if you plan on switching ROMs. Different roms have different feature sets and different feature sets. You can backup user apps and data using titanium and than restore them into the new rom (don't do this with system apps or system app data (these are the apps that come preinstalled) because it causes problems). Welcome to AC and Enjoy your stay!