This is a very important question that we are asked on our support forums often. So we thought it was a good idea to address this in our blog.
Technically speaking ours is a WordPress plugin which runs inside your main WordPress site. The users are registered in default WP tables and of course some of our custom tables. So the limitation on the number of users that can be supported by our plugin is actually dependant on the WordPress platform. We are yet to come across an authentic source of information which lists the technical limitation of WordPress regarding the maximum number of users that it can support.
Also in our opinion the number of users in a database is not really important. Let’s say you have a Site 1 with 100,000 users. But out of those users only 500 users are online at any given point of time. On the other hand you have a Site 2 with just 10,000 users out of which 2,000 are always online at any given point of time. The technical requirements in terms of server hardware and bandwidth for Site 2 would be very different from that of Site 1.
So in our opinion what is more important is number of active users that you foresee on your site. Technically there is no real limitation to the number of users that can be supported by a WordPress site.