We just migrated our Microsoft SQL Server from 2005 enterprise to 2008 standard on the same specification hardware. The databases were backed up and then restored to a clean sql 2008 install. The compatibility level is currently at 90 (2005). None of the Enterprise features were being used on 2005 (thus the edition downgrade). We have noticed about a 10-12% CPU utilization increase on 2008 compared to 2005. The only other change was that the SQL 2005 was running a server 2003 x64 and 2008 is running server 2008 x64. We aren't using any full text indexes.
Would the database compatibility level affect performance? We haven't rebuilt any indexes or updated statistics, would that have an impact? What else should we look for that could be affecting performance?