GWT Pros and Cons

Pros:

• no need to learn JavaScript (yay!)
• you get the fast productivity of Java => resulting in a faster and more optimized JavaScript than what you would have written by hand
  
• no need to worry about browser quirks
• using statically typed language (Java) to develop the client-side of the app allows to catch various problems even before the code is compiled (tools, IDEs, static analysis tools are available)
• debugging tools like any other Java app (can set breakpoints and debug the app in hosted mode)
• sharing the same language between the client and server (ability to use a shared Java package)
• hosted mode (you can make changes in Java on the fly and just hit "refresh" in the hosted mode browser)
• generics in GWT 1.5 (better static type checking on the client part of the app)
• DOM abstraction => code in one language and compile properly for any browser
• history support
• open source => many free widgets

Cons:

• only a subset of JRE available to use on the client side (translatable to JavaScript using GWT compiler)
• the concept of modules can get very confusing
• web indexing of Javascript is difficult, often developers need to create a HTML-only version of the app just to allow search engines to index it => hard to maintain, pain to write
• hard to the use a wider range of browsers for testing
• can not edit CSS while in hosted mode
• does not offer RPC mechanism using Comet

Comments

[Robert "kebernet" Cooper]

Comet RPC Implementation:
http://screaming-penguin.com/node/7661

If you wanted push style comet, you can just back the iterator with a blocking queue instance.