I suggest you go buy a Line6 GuitarPod. I bett you get way better sound out of that compair to a softwarepowered distortionsimulatar.
I wounder how people can be so excited about that Iphone application. I find it quite stupid.

But the best sound is always One Guitar, One Cable and One Tubepowered Amplifier from late 70's. That is Rock n Roll!
Trust me