747b0392__5_1___Postgres_OnLine_Journal__Microsoft_SQL_Server_2008
[Feature] Query Planner for complex queries (like doing correlated joins, lots of joins, lots of aggregates etc)-- the thing that figures out how to navigate data based on SQL Statement and histograms and stuff. This is off the cuff rating and varies based on kinds of queries you write. For the joe blow blog or CMS or plain read SELECt ... FROM, this is probably not important and all 3 will perform adequately. We do a lot of statistical and financial apps where ability to run complex queries against millions of records in under 5 seconds is important. [MySQL 5.1] Sucks Okay this was a spatial analysis and we can argue why beat a dead horse. But this is just a bounding box query. [PostgreSQL 8.4] Best. PostgreSQL doesn't support parallel processing out of the box, but supports shared reads and with GridSQL (which we haven't tried), you do get parallelism [Microsoft SQL Server 2008] 
Moderate (but supports parallel processing out of the box).
Cross Compare of PostgreSQL 8.4, SQL Server 2008, MySQL 5.1 - Postgres OnLine Journal
Microsoft SQL Server 2008