MR2 OSD has been Mar 2011 for some time now I think, no change there. MRA4 ISD was "late 2010" (mind you it has been a variety of dates from 2000 onwards I believe), and has slowly drifted now to Dec 2010. In addition I believe the definition of MRA4 in service has drifted from 6 a/c and x crews to 4 a/c and 4 crews. This was no doubt on the basis that we are only getting 9 a/c, not 12, 18, 21, etc, and - more likely in my somewhat cynical opinion- because 4 a/c and 4 crews is easier to achieve by the end of 2010! But that is just my opinion.
Late 2010 still being talked about here:
Nimrod MRA4 - BAE Systems
More recently:
PICTURE: BAE's first production Nimrod MRA4 gets RAF livery
I don't know how many MRA4s will be in service by Mar 2011, but then again, how many MR2s are left now, and will be left by Mar 2011?