I've been on it for 8 years - not for depression, but for panic, general anxiety and moodiness in general. It helps A LOT. I take 200 mgs. I also take Klonopin when I'm having a major panic attack, but nothing stops the complete meltdown situations, which are pretty rare anymore.
Someone asked about memory problems - this is going to sound like I'm being sarcastic, but I'm not. I have memory issues and I don't remember if I've always had that or not. I think I used to be able to remember things, and it might just be that I'm getting older (I'm 35), but people at work ask me what I did over the weekend, and I can't remember. I don't know if it's being put on the spot to answer (my mind goes blank when a question is directed at me), or if I just have memory issues. I think it might be related more to the fact that if it's something I don't really care about I don't usually remember it. I don't know.
Judging from that last paragraph, I'd have to say Zoloft has eaten my brain.