OpenLaszlo, for which I am the documentation guy, now compiles to DHTML as well as to Macromedia Flash (swf). That means that you can take the same LZX source and compile it to either swf or DHTML, and it will just work. So there is now a completely OpenSource stack for doing web apps.
OpenLaszlo is much more robust and full featured than any other Ajax toolkit. And, the architecture includes a client abstraction layer, which means that we worry about browser inconsistencies so you don’t have to. The upshot of all this is that if you want to build a real web application, you should use OpenLaszlo instead of some Ajax toolkit. Of course if you just want to spruce up a web page, Dojo or Rico or something like that might be appropriate. But I think you would have to be nuts to use them for building a real application.
We’re not yet shipping a “production” version — that’s scheduled for “sometime in 2006”– but the prototype version is getting more robust by the day, and there is a very credible demo up on the website.