Yesterday, Microsoft released SQL Server 2008 SP1 CU4, which is Build 2734, and SQL Server 2008 RTM CU7, which is Build 1818. There are over 40 included fixes in the SP1 CU4 release, across many different areas of the product. As I have said before, I really think you should be off of the RTM branch by now, if you are trying to stay relatively current on Cumulative Updates (which I think is a good idea).

One thing I learned yesterday talking to someone on the SQL Product Team is that they refer to Service Packs as Public Cumulative Updates (PCU) internally. Just keep that in mind if you hear some talking about PCUs.