Users have been posting repeatedly across multiple official mailing lists and forums asking why they aren't receiving updates. The situation, from a social standpoint, is chaotic.
The following update services appear to be impacted:
* csup and cvsup (for src, ports, doc, etc.)
* portsnap (for ports)
* freebsd-update (for binary updates / security updates)
* Native CVS
This issue also affects all FreeBSD cvsup, portsnap, and freebsd-update mirrors worldwide.
FreeBSD Project members have eluded to this being "maintenance", however no details other than that have been given at this time. The only known statements are as follows:
If truly maintenance, this work was not announced publicly in any way (e.g. the freebsd-announce or freebsd-stable mailing lists, forums.freebsd.org, RSS/news feeds, or the FreeBSD website), and as of this writing there is still no announcement.
Those natively using SVN are not impacted. This includes all of the FreeBSD developers/committers. Commits/fixes (to FreeBSD itself) are still being made via SVN.
Ken Smith of the Primary Release Engineering Team has stated in a recent announcement (preceding 9.1-RELEASE, which is not out yet) that the aforementioned services will eventually be deprecated in favour of using SVN and portsnap exclusively:
It is therefore speculated that some sort of infrastructure change may have been performed that relates to the cross-over nature of VC systems (e.g. possibly the SVN-to-CVS gateway on the back-end is broken), but as stated above there is no confirmation of that fact at present.