I'm very happy to be part of HTML5 runtime beta testing!
I made my very first test: the classic simple application of a single Active object, with bouncing ball movement inside a frame, bouncing against the edges of the frame. It works perfectly!
Like someone else reported, the application doesn't work in outside a webserver, so I'm using xampp.
BUG: In the application properties, the Build Filename property doesn't work: if you click the "..." button, to browse for a filename, nothing happens. Even after I've built the application, using File->Build->Application, and chosen the project path and name, this property in the application properties is empty.