I think the best I've ever done is to leave 3 balls on the table. And that was for a relatively low overall score because I didn't build a big-point block to explode. You get "breaker bonus" points for leaving less than 5 but it didn't seem like anything to write home about. Of course that was before discovering I was "master of the domain"
and my perspective was that I was being incredibly stupid and all the brilliant gamers out there were getting thousands of points in a game.
Anyway, I hope to stop the madness and clear the board someday!
In the meantime, maybe the real Jawbreaker god will log on and give us all a tip.