I've been trying it as well for ~2 months (with some gaps).

Normally I have trouble falling asleep, but have no problem staying asleep, so the main reason I take melatonin is to help fall asleep.

Currently, I take 2 5mg pills. Taking 1 doesn't have a very noticeable effect on my ability to fall asleep, but 2 seems to do the trick. However, I have to be sure that I give myself 7-8 hours for sleep, otherwise getting up is more difficult and I may be very groggy the next day. This can be problematic because sometimes I just have to stay up slightly later doing homework and because I can't take the melatonin I end up barely getting any sleep at all.

I haven't noticed any habit forming effects, though some slight effects might be welcome if it helped me to remember to take the supplement every night ;)

edit: its actually two 3mg pills, not 5mg. I googled the brand walmart carries since that's where I bought mine from, and it said 5mg on the bottle. Now that I'm home, I see that my bottle is actually 3mg.