Rollup 6 for CRM was released on Jan 12, 2012
Note that it was pulled back over the weekend but should be available again soon.
A Microsoft CRM 2011 Client for Microsoft Outlook issue has surfaced, and the Update Rollup 6 packages for Client and Server are being temporarily removed from the Microsoft Download Center pending our investigation. Please hold off on downloading Update Rollup 6 until new packages are available.
If you have downloaded UR6 packages for any components, please discard them and wait for an update on our investigation and the release of new packages. If you have installed them, please note that the issue appears to be related to Outlook Client sync and prepare to install a newer build when it is available”
More on that here.
KB Article: http://support.microsoft.com/kb/2600640
Downloads: http://www.microsoft.com/download/en/details.aspx?id=28712 (not working at time of post)
CRM 2011 SDK 5.0.9 can be found here: http://www.microsoft.com/download/en/details.aspx?id=24004