How large could a private server get,and what's the largest?

[swatch]

Because of the fact that all this was coded by individuals (the server code, that is), the game experience/quality is likely to be a lot lower than Sony's. Not anyone's fault really.

However, I do believe some of the private servers can hold a couple hundred people. Winter's Roar boasts that, anyways. And not all servers are going to be well run, or meaningfully run. IE, just up for a few people's enjoyment. Not catering to an audience.