Clickable: http://www.iosuserfeedback.com

I don't develop iphone apps but I immediately see value in the service. That being said...

I'm curious as to how you present the side-by-side view. Much of the content in the iTunes page is (directly) out of one's control (Customer Reviews, Customers Also Bought, Ratings etc). So you would be comparing primarily the logo and the description. It would be great if there was a way you could blacken out/shade the areas someone can't control so that what you can change (and therefore what is being tested) can stand out.

Good luck!