I have used it for developing an intranet project. For a single (kind of) browser and limited number of users. I liked it much because I hate the quirks of JavaScript.
It was about a year before and I did not check the new versions.
The flaws I would mention:
In case of browser incompatibility it would be hard to hack so I would not use it for public web page.
The Java to compiler was too slow so code-try-code again cycles were slow
The Java _like_ Language and system libraries were _very_ restricted.
Finding and including good libraries was not easy. I could not find good collections library for example.
Witout Java serialization and reflection real easy remoting to a Java web server is not possible. So you have to build and parse xml by hand. I really missed a good remoting framework based on interfaces and no hand coding.
Slashdot Mirror
It was about a year before and I did not check the new versions.
The flaws I would mention: