Agreed. All those flash sites do is misdirect people on what is a good design. If anything you can get an idea based off of it, but I think its always best to have the artist come up with the tattoo design. Most artist work better when you don't put them in a "box".
But I can see how an app where you can place flash on a body and play around with it, as a "game", would be interesting to people. But to use it as a reference for getting tattoos, might not work as good.
Just my opinion