"On paper, Rock and the T2 look like they'd be a very good match for Oracle's workloads, but since Oracle's license prevents publishing benchmarks and I don't have the hardware and software to hand to test them, I can't tell how they do in the real world."
I do have the hardware and software to hand :-). We moved to T2 architecture (T5240s) at the beginning of the year for Oracle and for a bunch of other apps. In the case of Oracle it does what you expect - scales massively well for large numbers of fast queries (i.e. typical webapp situation), but of course if you have a single huge query, it's going to run on a single execution thread, slowly. A simple performance test showed Oracle scaling linearly until our test *client* ran out of steam - by then we were far about any expected load so didn't test further.
The key thing is licensing. We run Oracle 10g standard, and it works out very well. Oracle have insane licensing with fine distinctions about when a core counts as a CPU blah blah blah. Right now, with T2 we get 64 parallel execution threads for 1 Oracle CPU license, which works for me :-)
I'll be interested to see what Rock offers, but with the virtualization capabilities in Solaris, the T2 gives us a lot of room to be flexible and split stuff up. If you've been paying attention for the last 20 years and have designed your software on the principles of atomicity, asynchronicity, and statelessness, it does let you scale very very nicely.