In summary, all products have changed a bit since their prior versions. The core changes:
PostGIS 1.5 has geodetic support now in the form of geography as well as some beefed up functions and additional distance functions like ST_ClosestPoint, ST_MaxDistance, ST_ShortestLine/LongestLine
SQL Server 2008 R2 basic spatial support hasn't changed much when compared to SQL Server 2008, but there is a lot more integration going on integrating Spatial into reporting services, Share Point and just integration
in general with SQL Server 2008 R2 and the Office 2010 stack.
Oracle 11G R2 - has finally offered an uninstall script for Locator folks who do not care to break the law by accidentally using functions only licensed in Oracle spatial,
but innocently exposed in Oracle Locator. If all that were not great enough, you are now allowed to legally do a centroid if you are using Oracle Locator. Doing unions, intersections, and differences is still a legal no no for Oracle Locator folks.
Oracle now provides Affine transform functions, which have long been provided by PostGIS and have been available via the MPL licensed CLR Spatial package of SQL Server 2008.
I still haven't figured out where this R2 convention started. I thought it was just a Microsoft thing, but I see Oracle follows the same convention as well.