Last week KendoUI officially leaped to the rescue, offering to simplify UI development across platforms.
KendoUI's promises run alongside HTML5's run-once-run-anywhere ambitions, but also directly address one of the major concerns of HTML5 skeptics: performance.
For UI in particular, performance is crucially important: for an interface to feel natural, just a milliseconds can make a huge difference. KendoUI accordingly claims high performance across their whole toolkit, taking advantage of e.g. CSS3 hardware acceleration for animations.
Frankly, the real reason I'm writing about this is because I'm super-impressed by the demos' performance. (The API's look very simple too, but I haven't built anything with them yet.) Assuming they work reliably, their speed means that they should prove extremely useful for many web applications.
Check out the website, along with the blog (full of useful announcements the beta process). Or view the launch webinar (also embedded below), which is quite long (73 minutes) and a little drawn-out (especially toward the beginning), but captures some of the energy the project seems to be radiating.