I thought this was mentioned once before, but in case it wasn’t, backups of all public posts exist at ifarchive.org. This happens once per quarter. Each backup includes the posts since the beginning (not just the new stuff), making it possible to get historical views even if old posts are later edited or deleted.
Private messages, private forums (such as for the IFComp authors) and user account information is not included. The .zip archive for each quarter contains a single large text file containing all posts.
Also, the ATOM feed for the forum is available here:
As with the backup, this includes only the public message boards.