Great idea but.

Sure its extremely hard finding a good singing app on iTunes, but the loading takes a bit of time on my 4S and have you guys noticed how your vocals are slower than the original or lagging throughout the song?

If this app adds iTunes lyrics to the songs too, itd be a killer app. Plus maybe we could hope for better microphone equipment on iPhones.
Overall, Id say yes, but only if youre desperate, and contempt.

Blahlalalala about Singulaa by Tunedra