Being an internet denizen from the old days of Usenet I've long been a forum participant. Each one has it's personality, and unsurprisingly they tend toward gross manifestations of temperament.
SP Forums: These are filled with people making jokes (and thinking they're being funny) and light conversation littered with supposed information. Invariably I end up correcting the false information and bad advice, and invariably the natives get pissed at me. So my membership doesn't last long.
SJ Forums: Usually ernest and with some humor. The down side is the same posts appear month after month, with nothing new ever to be seen. I implode in a cloud of silent boredom, and so my membership doesn't last long.
NF Forums: Lots of hugs and kisses and emotional support. I can't seem to find a steady raft in the sea of emotion, so my membership doesn't last long.
NT Forums: These are either INTJ or INTP, I haven't seen the ENTX's get much together. The INTJ forums are so boring and intellectually dry I just wilt, so my membership doesn't last long.
INTP forums are entirely different, with the exception of INTPCentral which is more depressed ISTP as far as I can tell. Conversations are interesting and diverse, with both information being exchanged and lively discussions. The proof that it's not just me is that they attract a wide range of types, except the ESXX's AFAIK. Here be welcome everybody from ISXX's to INXX's.
The worst thing about the other forums is that in many of them, such as financial forums, purport a zeitgeist where if you don't speak in the same language you will be ousted. I never speak the same language.