Microsoft has a new KB article describing a problem where the MAXDOP setting that you specify (whether at the instance level with sp_configure or at the query level) is ignored by SQL Server 2008, unless you set it to 1.
The MAXDOP setting controls whether and how SQL Server may decide to parallelize a query by running it on multiple processor cores. If you have an OLTP workload, it is pretty well accepted common wisdom that you should set MAXDOP to 1 at the instance level, so that SQL Server will not parallelize queries (unless you override it at the query level with a query hint such as OPTION MAXDOP (1). I have had very good performance results at NewsGator running with MAXDOP = 1 at the instance level.
People who have non-OLTP workloads usually run with MAXDOP set to a higher number, since long running report type queries can often benefit from being parallelized. They are the ones most affected by this bug, which is corrected in SQL Server 2008 SP1 CU3.
