Don't know if any of you are into video games or the Play Station Portable specifically but there is a new homebrew app that looks pretty neat.
http://www.psp-hacks.com/2007/05/11/guitarbox-152-real-time-guitar-effects-processor/
"A working class hero is something to be..." -J. Lennon
It is a good reason to downgrade my PSP...
Nevertheless, IMO, the most useful option is not implemented yet: the guitar tuner.
PSP Guitar tuner is the application for the rockstars. It is Homebrow application by ZION.It is the application that allow you to play a string of guitar. So you feel like you are playing real guitar. Now I can tell you its controll. Start button navigates you through the menu, while Select returns you to the main menu, and the buttons as displayed plays the required tone. Simply select which set you want to tune to via the menu, then follow the onscreen instructions to tune your guitar. It is not Upgrade Degrade issue, Its the passion about music.