I've used it before, off and on. I've not been taking it lately, and I probably should start again. I would start by taking 100mg a night at bedtime. It might give you some weird dreams and/or help you sleep better.
What I noticed is that the effects build gradually over the course of a couple of weeks, but then you hit a plateau of sorts. I imagine that upping the dose would increase the plateau, but I won't go over 100mg because I don't want to cause any serotonergic problems (I take Desoxyn daily at 20mg, and it actually exerts a very strong effect on serotonin). You should notice the effects within a couple of days of starting, but it's just going to be that you wake up and everything is just a little better every day. The sun shines a little brighter, theres a little more of a bounce to your step, etc. It's not a miracle drug, but I think it definitely can be a useful tool in mild-ish depression. For severe depression, I couldn't say. One thing I noticed about it (although I can't say it was the 5-HTP for sure, as I had recently started my Klonopin and Temazepam Rx's) is that in the mornings, for about the first hour to two hours after I woke up, my emotions would be all screwy. Like, I would be walking to work and listening to my iPod, and a song would come on and it would make me incredibly sad, and the next song would come on and it would make me all pumped up and ready to take on the world. It was weird, so I stopped taking it.
That only lasted an hour or two every morning (from when I opened my eyes, so this includes showering and all that; it shouldn't affect work or school or anything it's just annoying), but the rest of the day I was in a good mood.