Just Google my name and you'll see pages and pages of my various posts from a decade ago. Amazing how long stuff stays on the internet. Something to note.
I've gleaned fabulous facts and even made real life friends from these forums. I don't use them so much any more. Not sure if I've just wrung every drop of information or if my research has matured past that or if no one uses them as much any more. Probably all of the above.
Of course there are the message boards on Ancestry.com (which gobbled up Genealogy.com and Rootsweb.com message boards) as well as those on various other sites. I've recently discovered the genealogy board on City-Data (which is an awesome forum in many respects...not just genealogy). It's very general and while I won't find any family information there, it's excellent for discussion, advice and the like.
Even Reddit has ingrained itself into the genealogy community.
Naturally Cyndi's List has a category for message boards.
Have fun checking it all out! I dare you to stay up all night engrossed in the message boards...as I have on many occasions.