I'm not a JS expert but judging by the questions on S.O. I had the impression that few people had bad things to say about jQuery. Was not aware of its 'fragility'. Good to know.

You say: "GWT seems like a platform for Swing programmers who don't want to deal with JavaScript's idiosyncrasies and browser quirks." But couldn't you say the same about jQuery?

In fact, GWT requires you to understand the DOM and to get into the more advanced tricks with GWT there are features to let you write js directly in your Java code.

Not sure what you mean by "ease data transfer": "If you're doing a lot of data manipulation and storage with AJAX, GWT may actually be the way to go". Do you mean if your ajax passes a lot of data back and forth, then GWT might help because its minified and optimized?