Yep - you heard me right!  Update Rollup 1 has been officially released!  You can download it here:

http://www.microsoft.com/downloads/details.aspx?FamilyID=57c6267b-3b13-49dd-bfed-3cc83633aea7&displaylang=en

Some things to note:

1.  Obviously, you'll want to back up your system and databases before you apply this rollup
2.  Secondly, I recommend reading everything posted about the rollup - including fixes that must be manually applied, or require more steps be taken.  Here is a good start:
     http://support.microsoft.com/Kb/952858
     This link also lists which fixes are included in this rollup
3.  Third, I highly recommend you apply Update Rollup 1 in a Development environment before you throw it in Production.
4.  Microsoft is not recommending (or supporting) you import customizations in to a CRM 4.0 system where
     a.  The source system has Update Rollup 1 applied, but the destination system does not
     b.  The source system DOES NOT have Update Rollup 1 applied, but the destination system does
     I've not attempted this myself.  I know the import would fail in the 3.0 days - not sure if that is the case here?  Just good to know and follow this advice
5.  If you have customized your help files, you must back them up prior to applying this update
6.  The update for Help files is not included in the update rollup.  You can download the most current updates for Help files here:
     http://support.microsoft.com/Kb/KB955921
7.  As with previous update rollups, there is a CRM Client update rollup to apply as well
8.  There is also a CRM 4.0 Email Router update rollup to apply this time around
9.  You do not need to apply the server and client fixes at the same time.  I would recommend you apply them to both environments - but it's not like you MUST update the clients the moment you update the server, or vice-versa

Happy downloading!