Wow, there are a lot more of these online than I would have guessed. Over a thousand. Feels like it would take forever to find one with a regular active user base. My off-the-cuff guess would be that 99% of them are ghost towns, kept online by the sysops only for the nostalgia factor. (But I'd very much like to be wrong about that!)

Related: I'm (pleasantly) surprised to see the rash of BBS-related content on HN recently, as I've been working on my own (rather niche) BBS retrospective article for the past month or so.