See
http://realityismyreligion.wordpress.co ... open-soon/ for an insider perspective.
I wasn't a big user of the RDnet forum, I found it too large for my liking, but thousands of people did (hence the too-largness I mentioned), and it seems it was shut down merely because the site admin had little personal interest in the discussion forum even though it's by far the most popular - and for my money the most useful - part of the site. The rest of the site is largely a collection of links relevant to atheism, science and Richard Dawkins himself. There's virtually no original content.
It appears that some users have had their accounts - and with them thousands of posts - deleted, never to be recovered. The lockdown means that people won't easily be able to coordinate moving to other forums or to find each other. Three years worth of posts, millions of words, look set to disappear forever.
All in all, I think this is a very bad move. Hopefully, common sense will prevail and the forum will come back up, or at least remain as a searchable archive.