Steve -- love the site. So, it was very clear that MS is working on scale-out for the release after Katmai at minimum; they announced this at PASS. I'm curious as to their architecture.
The problem with Oracle RAC is beyond it's cost, it barely works cause it relies on synchronizing the locks for the shared disk. SQL Server is shared-nothing so they are off to a better start. So Oracle RAC is a scale-out solution for HA if you ask me, not scalability. Oracle experts will tell you that you have to change the application and avoid the load balancer if you want it to scale. I could go on, but just look at some of their benchmarks on the same machines that were clustered and then unclustered and you can see. One of the TPC-H ones come to mind, their TPC-H 10 TBs from a bit ago. Good example since it is the same machine. From 1 64-way to 2 64-ways with RAC they go with 76% scalability (not nice when $10,000 of every $40,000 gets you nothing) and costs were 36% more -- pay more go slower. Nice! OK, so you get I'm anti-Oracle. I'm not anti-Oracle, I'm anti-BS! RAC is an HA solution and quite frankly I think MS MIRROR gives you all the same availability and less complexity (#1 reason for downtime).
Furthermore, note that Oracle RAC only protects you against S/W error; what happens if the disk goes, that high speed switch, and more. You're done. No disaster recovery unless you mix it with Data Guard -- now you're talking mega!
So to me -- scale out is great if you use it for BI. For OLTP, someone show me what SMP can't handle your workload vs all those hundreds of gyrating parts in the blades for HA. Don Burelson (world's leading Oracle expert) agrees! He notes:
"Unless you are one of those shops that have a need in excess of half a million transactions per minute you are probably going to find yourself in a scale up environment."
So I'm going on too long.
One thing about ParAccel. I could be wrong here, but it's column oriented and the one thing wrong with those databases is the insert and updated performance. So when you think about real time BI and such -- the story falls apart. Compare it's disclosure in TPC-H for the queries that have such activity with relational and you'll see what I mean.
Wow, that's a lot of text to say the MS is working on it.