The ASP.NET AJAX library is one very cool, performant work of engineering that has smoothed the programming experience for web developers, and now they're taking it to the next level.
Dino Esposito writes about Live Data Binding in ASP.NET AJAX 4.0, and shows how some of the cool tricks are pulled off to get things like two-way data binding. Definitely worth reading.
Funnily enough, he references the mechanism introduced by IE4 to do data binding, and yet even today that's one of the top hits for "html data binding" on popular search engines. It's good to see improvement in the space, and kudos to the ASP.NET AJAX folks for giving us a good cross-browser solution.