Just for kicks I've been writing a new website (the previously mentioned taskify.net) and to a.) Increase the usability of the UI and b.) just learn more about ASP.NET AJAX, I've been implementing a lot of the AJAX controls into the site. I've got to say, I think Microsoft really hit a home run on this one.
I'll admit, at first it's very hard to grasp the concepts you must put in place when working with AJAX.NET, but much like .NET as a whole, once you figure out the patterns and the practices used to develop the tools, it's easy to pick up on all of the tools. You'll never know how satisfying it is to refresh the data in a GridView without a full page refresh until you try it :-)
Head over to http://ajax.asp.net to check out the AJAX Extensions and the Control Toolkit. You can also click the button below to see a live demo.
