As one who lost ten years of her life to depression, I can certainly sympathise with what Zach
has to say. However, I think there's a degree of confusion
I don't think it's depression itself which has become fashionable, but the trappings of depression - the paleness, the sunken eyes, the mournful gaze, the lanky hair, the cadaverous thinness (although anyone who knows anything about depression will tell you that none of the above are necessary or even common symptoms).
It stared in the early '80's with Goth fashion, which still survives today, and was added onto in the '90's with what the fashion mags termed "heroin chic". A lot of clubland fashions also contribute, and of course the waif requirement is universal.
Personally I think that if people want to look like they're sick, bully for them. I like to look and feel like I'm healthy - rosy cheeks an' all. But I can't say I'm somehow offended by these juvenile theatrics, could you?