http://www.flohofwoe.net/demos.html, these demos are about 150k to 250k lines of C++ code, and are about 700k to 1.5MB downloads, the same as zipped native executables. I'm also on the team which does a web-based MMO which is running for 3 years now (not done with emscripten though), so I'm aware of the problems :) It's still miles better then closed platforms.