Although this guy DOES have some musical skill, this app is more of a gimmick than anything. I play several instruments, including guitar, bass, drums, and I can carry a bit of a tune as a singer, and I have a friend who's on the same page as me who owns an iPhone.
This app uses AUTOTUNE.
Auto-Tune - Wikipedia, the free encyclopedia
You may recognize this if you're a fan of R&B/Rap. They like to use it a lot.
It corrects the pitch and makes it all in tune. Doesn't really take much skill.
I'm not doubting that it'd be fun to play with. My friend downloaded it, and has informed me that you can use it to create your own songs, so you're not stuck with a library of songs that someone else wrote, but in the end, it's smoke and mirrors...