I was diagnosed right around two years ago with Major Depressive Disorder, and shortly after ADHD (which my parents knew about but never had me treated for), which is largely why I stopped posting here. My doctor told me that, given all that came out in therapy sessions, I had been dealing with both since childhood, and that the ADHD can make the depression worse. It got really bad shortly before my parents forced me into therapy.
I was diagnosed with an anti-depressant (can't think of the name of it, off the top of my head) and adderall (for the ADHD) a little while later. The anti-depressant largely did what has been stated here in this thread: it made me numb and flatlined, which bothered me. I didn't hate anything or feel depressed, but I wasn't happy and having fun either. However, the adderall did help greatly with both, and while I'm not sure if it's intended to help with depression, it did in fact help, and for a reason:
It motivated me to do stuff. I got up early, went to bed at a decent time, and I was very active throughout the day and didn't want to sit around wasting time. That's how I had been all throughout high school and the earlier years of college, as I was on a few sports teams and did a number extra-curricular activities. That kept me busy and it kept my mind active- I never really had time to be depressed (my docs also said activity will help combat depression biologically as well). I also found a new college that supported the degree I've wanted all along, and it got me working on one of my dream jobs (which I'm working toward), and that helped boost things a lot, especially when I began seeing results.
With that in mind: Put simply, do stuff. Be active, do stuff that you're interested in, go out with friends, don't let yourself say no. And as Matt said, talk to friends and have someone there when you're feeling down. Hell, even if no one's within the reach of a phone call at the time, you've got a whole forum full of fellow super geeks here, right?
And, as hard as it'll sound when you're having your downswings, as Matt said as well, remind yourself that you're never alone. Not like, "Suck it up, others are more depressed than me," but more akin to, "Others with my problems have great lives and get through the days just fine, I can too."
Go out and do something! Accomplishing stuff will be a huge boost, even if it's just something like learning to draw better than you could before.