Before LJ, all my fandom activity was on messageboards and I far prefer LJ. I like having my own space while also being able to easily interact with others through communities or posts in individual journals. And as others have mentioned, threaded discussions FTW (and comment emails and tracking and all that stuff which is making it even better). And I really love that everything is in one place. Before if you were multifannish, that involved joining a bunch of different messageboards or mailing lists, and now everything is just right there on my flist.