Microsoft is WAY behind the curve on this topic, and PDW will take at least another 18 months or so to be anywhere close to where it should be. Oracle Exadata is doing very well in the marketplace I think, although I think part of that is very aggressive sales and marketing tactics.
It is definitely a tough problem to solve, but I think PDW will get there eventually. The Datallegro IP (and people) they acquired are good.
Kevin G. Boles
SQL Server Consultant
SQL MVP 2007-2012
TheSQLGuru at GMail