I rest my case...

I have certain friends, one of which is actually a singer, who says Beyonce can't sing.  Well, um...

Jay-Z Films Beyonce Rehearsing “1+1″ Backstage @... by thehiphopconsultant

...let's just consider the case closed.

For those who can't get enough... here's the actual American Idol Performance that she was rehearsing for: