I was on Roaccutane 20-40mg doses for around a year (quite a long course as I was yo-yoing with depression, so they kept messing with the dosages...)
It definitely helped until around 6 months after the end of the course, after which time it began to come back and that's where I'm at right now.
Personally I'm very reluctant to go back there... I suffered severe Depression and a nervous breakdown subsequently - whether this was the drug or just an inevitibility I'll never know - but you can see why I'm not fond of the idea of going back onto it.
I'm just getting back to semi-normality now with regards to my moods, however I'm told I was a nightmare whilst on Roaccutane the last time (anger, mood swings etc)