I've got stretch marks not from muscle growth, but from fat growth...they don't go away when you lose weight, all they do is fade.
I bought mederma, but I'm pretty bad about routines like that so I quit applying it and I question its effectiveness anyways.
I was alarmed when I saw deep purple ones cropping up, but now I don't think they're a big deal at all. It's not like they'll make someone more attractive, but they don't detract from someone's appearance.