No, I opted against that, because sometimes they cause extra problems -- by not co-existing gracefully with GWT's panels or events, for example, or by causing testing problems with widgets that actually are a composite of several widgets. I did a project using such libraries, and went through one after the other, having problems which only got solved by going back to "100% pure GWT".
Hope this helps!
Great fan of Open Source, Linux, and web development with GWT; all of these come together for my ESSENTIAL GWT book!
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