Software that is designed to be multi-threaded will see the 2x-3x improvement in performance. Software that runs on only one processor will get only a small improvement.
Right. The system as a whole has a 2x-3x aggregate performance improvement (how many things you can run at the same time how fast). That's not to say for any one particular program running by itself that it will go that fast -- it may, but of course, performance varies. And he did make the claim about the specific benchmarks -- just like all his competitors do. He was very clear they were benchmarks and in fact that all benchmark numbers are a little exaggerated (if you watch the video).
On the other hand, I was in the store and played around with one for a few minutes over the weekend and it certainly SEEMED very fast for interactive usage, even for things running under Rosetta. So I don't think that its speed will particularly disappoint anyone.
On the other hand, it's certainly fun to try taking down Steve Jobs a notch :-)