Even though I like to talk about the most recent major releases of SQL Server, there are still plenty of organizations running SQL Server 2008, which was a good, solid release of the product, with many improvements over SQL Server 2005. Lets assume that you have been pretty diligent about keeping your SQL Server 2008 instances up-to-date with Service Packs and Cumulative Updates, so you find yourself on SQL Server 2008 SP3 CU5 (Build 10.0.5785), which was released back on May 21, 2012. Actually, you should be pretty proud to only be on a build that is about seven months old, since I regularly see people running builds so old that they are on “unsupported service pack” levels, often being 18-24 months old.
You want some specific justification and ammunition for applying the latest SQL Server 2008 SP3 Cumulative Update, which is CU8 (Build 10.0.5828), that was released on November 19, 2012. You could read the fix-lists for each cumulative update since SP3 CU5, available from this master CU list article from Microsoft:The SQL Server 2008 builds that were released after SQL Server 2008 Service Pack 3 was released
Or, you can start out with this filtered list that I put together:
SQL Server 2008 SP3 CU6 (10.0.5788) July 16, 2012
SQL Server 2008 SP3 CU7 (10.0.5794) September 17, 2012
SQL Server 2008 SP3 CU8 (10.0.5828) November 19, 2012
Most of those hotfixes seem pretty significant to me (and this is just the subset that I picked). I strongly encourage you to start reading the hotfix list when new cumulative updates are released, because there is a lot of good information there. SQL Server 2008 SP3 CU9 should be released around January 21, 2013, which is good timing after the holiday freezes and quiet periods for many organizations are over.