I found 'success' with 24mg (September 2011), but in the last 5 months, I've also enjoyed 18mg, 12mg, 6mg...and sometimes even 0mg. When I can't sleep, I use 0 to 6 mg, but mornings are anywhere from 12mg up to 24 mg; depends on my mood.
I think my sweet spot is 12mg, but ain't nuttin' wrong...