I was looking at Thinlet last week. I didn't write it up as I was still a little peeved about my experiences with XWT. Thinlets use a nifty scheme of XML to describe the presentation and Java to do any logic. The demo was a little flawed under Linux with some event problems but it was generally very impressive in size (26KB) and features. It is just one giant file with lots of non-OO code in it. It's written for Java 1.1 and is designed to support light Java clients such as PDAs as well as browsers. Something that another toolkit has been aiming at too. One of the things that did annoy me about XWT was the scripting side of things. Being a lazy programmer you sometimes get dependent on the compiler to pick up some errors (like variable mispellings).
AWT is thread safe and there are differences across platforms between Windows and Linux, for example. Debugging threading issues is a problem, debugging OS dependent issues is doubly unfun. In the article about what to through away in Java AWT was one of them. An under OS X AWT objects are not hardware accelerated and they suggest you use Swing.
The use of XML to describe user interfaces is something that I think Java developer deserve. Just not this. For example, an RSS feed viewer in an hour. Then a friend of his wrote a resource editor.