Actually, the most frequent cause of the scarring that leads to a curved penis is circumcision. Despite the doctors that insist it's a very simple procedure, it's actually very easy to screw up. Guys end up with curves (which I also agree is not a problem; one of my boyfirends had a downward curve. His current wife is very happy), little scraps of hanging foreskin, and occasionally even have to get reconstructive surgery or are turned into girls.

And for what? There's actually no good reason to do it unless you're Jewish.