What big products? The only one that I know of is blogger. Google also recently stopped supporting it and made it an independent open source project, which is a mark against it.

I'm not sure where you got the idea that the compiler was advanced - what it does is amazing but incredibly slow.

The development tools were fine in 2008 but they're showing their age now... the browser plugin only runs in Chrome, Firefox and IE, and it's only fast enough to be productive in Firefox. There are no browser plugins for Safari or mobile and doing a compile to a WAR can take minutes on a big project, which means development for mobile can be glacial.

I've just worked for a year on a big GWT project... it seemed like a good idea to start with but I've grown to hate it over time.