About 7-8 percent sounds about right. Just thinking about it informally, if anyone is making a significant amount of money, then there must be a lot of people donating to the pot since I think most losing players don't lose very much (they simply quit playing or move to very low stakes). I do, however, think that 10% of those who try becoming winning players must be too low. It takes nothing more than a tiny amount of common sense and some patience to beat the micro limits. I can't imagine that anybody who wanted to be able to do this wouldn't be able to.