Here's my personal summary.
- Oracle holding on to 2nd place for enterprise data warehousing with its "reference configurations," Exadata product, and 11g upgrade as prominent strengths; downside being claims of higher DBA FTE cost than some other DW platforms.
- Teradata remaining the clear leader and probably expanding their market presence with newer pricing model and platform options.
- Microsoft lagging far behind the other big vendors while it tries to integrate the technology it purchased with DATAllegro in 2007.
- My favorite aspiring open source vendor, InfoBright, sitting in the middle of the of the niche quadrant as a brand new entrant.
Full disclosure: I don't own stock or have a personal stake in Gartner or any of these companies. I've personally developed or managed large data warehouses on DB2, Teradata, and Oracle.