Gah. People please stop using Z as the default key for down (or whatever). If you can't detect my keyboard layout use keys that are the same on every keyboard, no matter the language, or provide an option to configure the keys. My Z (on a Slovenian keyboard) is where your Y is (on your English keyboard).
This makes the game unplayable for me, since my "down" key is above my "up" key, which makes it almost impossible to play. /rant over
Awesome demo tho. Would love to see source of the flash part (maybe I missed it) so we could compare the source, not just performance (which seems to be about the same on my 5 year old laptop).
edit: who's now working on a (HTML5|Flash) vs Silverlight demo? That would be even more awesome.