The former board can be reached by going to: www.gettingthingsdone.com/forum_list.php
On your second question - my guess is a number of people are visiting but not registering. I don't login everytime I visit either.
I for one am very happy with the board, particularly since the software changes. I may be guilty of not posting often, but I see new posts every day, and many of them are very useful.
Thanks to everyone for sharing their ideas on GTD!