I'm not sure Javascript will ever take over as a preferred technology for browser-based games. I have always seen Javascript games and advanced effects as more novelties than anything else. It is a great language for enhancing user experience for web pages but I can't think of a reason to use Javascript instead of Flash for an identical task given the current support for HTML5 and the performance of js right now.

The HTML5 specification brings a lot of cool new features that may have me eating my words if it's ever fully supported by all major browsers, however, right now advanced js creations are better suited for the demoscene than the mainstream.