I think the point of these optimizations is that they allow javascript-intensive applications to be developed that would otherwise have just been too slow.
In other words, they're paving the way for the future more so than trying to squeeze every last ounce of speed from current applications (which just happens to be a great side effect of their work).
Yeah, you won't see a lot of applications that benefit from these optimizations immediately because if there were any that would mean that they had been written before there was any device capable of running them.
In other words, they're paving the way for the future more so than trying to squeeze every last ounce of speed from current applications (which just happens to be a great side effect of their work).