The speedup is substantial, at least in this case. Biolab Disaster has to draw lots of small 8x8 pixel squares (about 500 for each frame) to produce the background map - which seems to be awfully slow in the iOS browser.

Running in the browser, I had about 10 frames per second as noted in my previous blog post: http://www.phoboslab.org/log/2010/09/biolab-disaster