Actually, I'm not so confident about the ballpark. My link also says there are about 1.3 billion unique visitors per month. So in addition to 20 million Reddit

Actually, I'm not so confident about the ballpark. My link also says there are about 1.3 billion unique visitors per month. So in addition to 20 million Reddit 'addicts' there could be 1.28 billion less-frequent users. If they are worth on average $0.01 per month that would be an additional $150 million per year in revenue.