ArcGIS 10.1 is going out to pasture (Retired status) in the new year.
This was a really important release, this was when 64 bit Server and Desktop BG x64 (10.1SP1) came in. This release brought us arcpy.da and most of what's in the current arcpy and model builder world, and was the release when the metadata editor and framework was pretty much complete.
Thank you, 10.1 team! You gave us a great run.
UPDATE: just posted -