I have a weird experience with melatonin. It puts me out quickly, but I wake up about 4-5 hours later in a half drugged state. For the next few hours I'm awake but drowsy.
The next year I got 0.1mg tablets, experimented a bit and found that 8 of those (0.8mg) was the sweet spot for me (taken about 2 hours before I want to sleep). I generally used it in the winter, when it gets dark at 16:00, which apparently can throw my cycle a little out of whack if I don't pay attention, the melatonin seemed to help to fix this a bit.
I have to say, I've never noticed really strong effects like "puts me out quickly". Just a general feeling after an hour or two, that "yeah I could sleep". If I listen to that feeling, I sleep very well. If I stay up anyway, it goes away again, and I don't really get the benefits.
One thing I noticed, after a few weeks, was when I knocked over and broke a glass of water for the third time. I wondered, "hey that seems to happen quite a lot lately..". And always in the evening after I had taken the melatonin, so I guess it does do something to my coordination or perhaps alertness. This was easily solved by taking a bit more care where I place my drinking glass after taking melatonin :)
right now i take 1/2 of 2.5 mg melatonin (sublingual) with 50-100 mg 5-HTP, ideally 30-45 min before going to bed.
adding 5-HTP was A MIRACLE ! after just a day or two i slept very soundly and had AMAZING dreams – we're talkin 2160p 10.5 THX Lord of the Rings epic trilogy with you playing lead role. those first few weeks i even went to bed earlier just so i could dream longer. :) prior to that it had been decades since i remembered having any dreams. (warning though, i've told several friends about it – after they tried it they had to stop because the dreams were too intense.)
i read about 5-HTP in this book i borrowed from my chiropracter: http://smile.amazon.com/5-HTP-Natural-Overcome-Depression-In... basically it states that melatonin is only part of the sleep equation, seratonin is the other part. your body can produce seratonin from 5-HTP (which is the chemical in turkey which makes you drowsy).
also:
staring at a computer screen can really mess with your sleep – due to chemical imbalance with these hormones. to help as much as possible, i installed F.lux on all of my computers.
i also recently added Modalert to my daily routine, but that's another story...
As an aside, I would definitely say get your sleep cycles right and more disciplined definitely puts you in a much higher efficiency bracket. Coupled with some simple lifestyle hacks ( playing a team outdoor sport, if you are not the workout type, no devices in bedroom rule, boring but informative tech talk to go to sleep, light and early dinners, no coffee post sunset) you would be surprised how many extra hours of high concentration work you are capable of.