People here wrote they experienced about 40-80 chatters maximum. But this limit means it is not usable on sites where comes more people. It is pity. I am not curious to test the chat on server I am not the owner of server and want not to make problems. So you don't have experiences with 10-20s refresh? I think this could increase the number of chatters but don't know how much.
Anyway I want to ask about cache. I know that in the data/private/chat are hundreds of files. Why author saves every single information to separate file*? Would not be better for performance to save the data to a few files (few for every user or every channel). I'd like to have a chat with about 90 rooms and for about 150-250 chatters (I now this is not realizable for now). But I think that so many rooms and so many cache files could make problem for server...
Edit:
* - I heard about SQLite for PHP5
http://www.php.net/manual/en/book.sqlite.php
Which would simplify the process of saving and reading data from cache/chat ... and increase the performance. This look like much more better idea then hundreds of files that server have to look for and read informations about them.