[btipling]

I disagree. RSS readers have a significant long tail expense per user. I worked at Bloglines. Pretty much every one of those free users have extra little RSS feeds that nobody else subscribes to that you have to crawl, handle invalid rss/xml for, update and keep unread status on. At scale, that is the most expensive part of operating an RSS reader, and it's not worth it.

[levosmetalo]

I agree with your point that keeping RSS user is not free. But, from the users perspective, RSS readers are a commodity. You can't sell them subscription unless you provide them a free ride to actually check and hook up to your service. The only reason that OP is successful is having a business model working is that he already has a large userbase which was acquired largely because it was free.