I don't particularly care about games. That pretty much leaves just malicious use of it for me. I'm also unsure of how it would work with a modal browser.
The fancy things that are done in HTML5 aren't that spectacular to me which is why I build my own webkitgtk with most of it disabled. Some things just don't need to happen at all. For example, Engine Yard spikes a CPU after a few focus events on it so that it can waste time and energy animating a silly island or whatever making the site basically useless (though I don't do Ruby at all, if any site I *did* use ended up doing something like that, it's an easy way to get me to search for something else).