One limitation you're going to run into is that the content of your
site will not be search engine friendly since it's all generated
dynamically via javascript DOM manipulation. For most people here who
are programming actual rich web applications that's not really a
concern. But if, say, you were writing a blog application (or a
company home page) it would be important to the users that the content
was searchable by search engine crawlers. Doing the whole site in a
traditional GWT way (loading content from Async calls etc) would
preven that from happening. You'd probably need to write some of the
code in whatever serverside language you'd prefer in order to show
existing/hostorical posts in the HTML when the page is requested so
that the content is searchable.