As someone who reads a lot more than she speaks, I find it very irritating to have to register in order to post on a message board. My instinct is to say nothing unless it serves to further the subject in some specific way. I don't flame, and I try not to post inanities. I may lurk on a board for months before I run across a post that inspires me to reply. It's truly a pain to have to go through the whole registration process in order to post one simple reply. By the time I've filled out the information, checked my email for confirmation, and clicked through the maze of "okays" and "I agrees", the thread has changed and my comment would be useless. I know that it will probably be another month or two before I have anything else to add, so the registration won't do me much good until then... If I'm still finding the message board interesting in another month or two.
I understand that message boards have turned into communities, with the emphasis on personal interaction and knowing one another rather than just trading thoughts and insight. (Witness the myriad of smiley faces available, which serve little purpose other than to add personality.) I understand that people in the community want to retain the sense of accountability that comes with registering. I just tend to feel that accountiablilty isn't as important as the freedom to be inclusive.
It doesn't bother me when unregistered persons post. It's no trouble to read one sentence of the post, notice that the author is being intentionally provoking, and then skip the rest of the post. I've read a number of interesting posts by unregistered guests, and find their thoughts are often refreshingly removed from the general pattern of thought found in the particular message community.
While I understand and respect the desire to know who's speaking, I personally prefer to allow the unnamed to speak in hopes of hearing something new and stimulating, rather than silencing all who will not name themselves first.