I posted the results of my melatonin use over on the Astral Pulse forums. I've recently knocked my dosage down from 20mg a night to 5-10mg a night. There seems to be a point that the melatonin reaches it's highest usage, then it has no more or less of an effect.

5mg: More comfortable sleep. No changes in dreams.
10mg: Good Sleep. More vivid dreams. Dream characters are more hostile. Lucidity attained most often.
15mg: Fantastic sleep. Less vivid dreams but greater intensity. Dream characters are very violent and will often attack if disturbed.
20mg: Heavy sleep. Slept for 45 minutes longer than usual. Vivid dreams (about the 10mg level). No lucidity whatsoever. Reguar dream signs are ineffective. Dream characters are not violent at all.
So from my experience, 10mg is the best dosage for me.