Mad haTTer's list of the symptoms of depression closely resembles those most knowledgeable people will give you, with one extremely important exception. Increased creative activity is NOT a symptom of depression. In fact, most people who fight or have fought depression on a long-term basis will tell you the opposite.
Depression is not just a sense of numbness or sadness - though those are of course symptoms. Depression is probably better described as a kind of spiritual paralysis, a sense of worthlessness, emptiness, exhaustion - all of which can inhibit the patient's ability to be productive or to engage in life-affirming activities (i.e. poetry).
Some people, who identify their symptoms as those of depression, wear black and write angry poetry and talk about losing their will to live - that is, their will to physically exist.
Not to say that those people don't have real problems or real pain, or that they're not allowed to play in the depressive swimming pool. It's just that if such a pool were actually built, those kids would actually have the energy to swim, where others would float or tread water. Or drown in it.
You are welcome to glamorize the symptoms of depression and idolize its famous sufferers. Those of us who've spent entire days in a fucking cloud - sleeping or staring at the wall, without a thought in our heads - don't really have that luxury.
There is no good depression. It's not sexy. It's not fun. It's not the new rock and roll.
Kurt Cobain and Hemingway both indicate in their final writings that they had run out of things to say, despite pop cultural speculation that genius is America's number-one killer and its casualties leave damn good-looking corpses. I do not believe these men, or any other suicidal, brilliant people, were more creative because they were depressed, that the combination of the two traits did them in. Depression is what kills. A lack of productivity feeds into that. You're still allowed to swim in my aforementioned swimming pool (or, if you'd rather) to shudder and cry in the bathtub with me), but please, check your 14-year-old goth sensibilities at the door.
(For further elaboration see Alcestis on the Poetry Circuit.)