Biggest GWT Pitfalls?

I'll add some points to the ones already mentioned:

• Databinding/validation. GWT doesn't have a databinding/validation support out of the box, although there are some projects on this area starting to emerge. You'll find yourself writing alot of this:

TextField fname, faddress;
...
fname.setText(person.getName());
faddress.setText(person.getAddress());
...

• Lazy loading. Since gwt is on the client side, lazy loading is really not an option. You'll have to design your RPCs and Domain Objects carefully in order to
  • send all your object data that is needed
  • avoid eager fetching all of your data
  • You'll have also to make sure that you will not send proxies/non serializable objects. hibernate4gwt can help you with these points.
• UI design. It is harder to visualize an UI in java (Panels, Buttons, etc) than in html.
• History support. GWT does not ship with a History subsystem, nor does it ship with any subsystem for nice urls or statefull bookmarking. You'll have to roll your own (although it has support for History tokens, which is a start). This happens with all AJAX toolkits AFAIK.

IMHO, GWT is missing a framework that has out of the box support for all of the issues mentioned on this 'thread'.

No major pitfalls that I haven't been able to overcome easily. Use hosted mode heavily. As you are using GWT-ext you will almost never need to touch CSS yourself unless you want to tweak the out of the box look.

My recommendation is to use a GWT "native" widget over a library one where they are close in features.

Re search engine indexing: yes the site will not have navigable URLs normally (unless you are only adding widgets to elements of a regular web site). You can do history back/forward functionality though.

We've had a very hard time marrying our GWT codebase with HTML web templates that we got from a web designer (static HTML pages with specific div ids that we wanted GWT to manage). At least back when we used it, we couldn't get GWT to integrate with parts of our website that were not coded in GWT. We had it working eventually, but it was a big hack.

One major pitfall is that sometimes you need to explicitly assign an id to what ultimately becomes an HTML element to be able to use certain CSS styles. For instance: a GWT TabPanel will only do :hover over tabBarItems when the tabBar of the tabPanel has been assigned an id and you specify a :hover on that elementId.

I wrote about some other disadvantages of GWT elsewhere, but they are already covered by rustyshelfs answer :).

I have done a lot of work on GWT recently, and this is wht i have to say:

1. CSS styling is tricky only sometimes, use IE developer tool in IE and firebug in Firefox to figure out what exactly is happening and you will get a clear idea of what css needs to be changed
2. You can use tricks to get google to index it. A very famous site is http://examples.roughian.com/ check its ratings at google. A far less famous site is www.salvin.in (couldnt resist to mention that), i optimised it to words: salvin home page (search google for these three words)

I do not know much about GWT-EXT, But i too am of the belief that there is no need to include Third party libraries.

Best of luck on your decision :)