I would see this as an opportunity. You have an app that has hit a hard limit in terms of number of users. It is clearly a useful app, otherwise it wouldnt be g

I would see this as an opportunity. You have an app that has hit a hard limit in terms of number of users. It is clearly a useful app, otherwise it wouldnt be growing. The natural thing to do is to make it a paid solution. You inform your users of the situation and say that in order to keep the service up and running you will start charging a signup fee of $1, the same as you would pay for a mobile app. Existing users however, get 50% off and only pays $.50. Give them a month to paypal it in and then another month of repeated notices to inactive users. After two months there will probably 50k+ users you will have to close out from the service. But give them an option to restore it easily. This is not at all unreasonable, no one would ever be able to say so. Above all it would be a tremendous learning experience for you. Perhaps you also will make a few thousand dollars in the process, but that would not be the point. There are two alternatives to this as I see it. Either you do the above but the only thing you require is for users to manually report in by clicking a button in a form. You will still be able to weed out thousands of accounts. The other is to set up Smart Tweets 2, hosted on another ip, and refer new users there. Explain why and make it into something funny for the users. Whatever you do, do something bold enough to make it to Techcrunch a second time.