Okay, it happened a couple of days ago; sorry for not noticing. But SQL Server Release Services / Sustained Engineering has announced that an SP3 Beta has been made available. The build is 9.00.4028 and you can download it here:
http://www.microsoft.com/downloads/details.aspx?FamilyId=D22317E1-BC64-4936-A14B-7A632B50A4CA
This is earlier than I expected, and is probably why, unlike previous cumulative updates, no advanced KB article was produced for CU11 after CU10 (9.00.3294) was released.