I've wondered what draws me back to them repeatedly and I don't think I've been able to quite pinpoint it. Besides the appeal of interacting with others whenever you choose (no worrying about schedule conflicts) why do you love message boards, and what do you hate about them?
I'm a bit of a message board slut myself
and MMOG is one of my favorites. Good conversation topics are a must. Often I find that topic-spam, and lots of 'i have a notion that...' ideas, bring good discussions, but with this things get moved so far down in the list and people won't see them unless they visit within a narrow timeframe. Having an intelligent community can help a lot when the posters are talking about things within my scope of interest, which unfortunately isn't very wide. A variety of posters from different backgrounds also helps, since my view is usually skewed by what I experience daily.