Stephen, at a high level, what is this patch for?
Basically fixing how GWT handles classes with "$" in them. Right now there are a lot of places where GWT assumes "$" can be replaced by "." to go from, say, a binary class name of "Foo$Inner" to a source name of "Foo.Inner". This is generally true for Java, but is not the case for Scala, so this patch was originally beneficial/required for Scala-GWT. However, that is no longer the case, as broken binary <-> source name conversion does not affect the current Scala-GWT approach. So, AFAIK, now the only things this patch affects are basic aesthetics (e.g. I think it's cleaner to avoid the s/$/./ hacks) and gwt-query since they could then use "$" as a class name to do more jquery-style things (...IIRC, there is a bug in the issue tracker about it).
How important is it for GWT 2.5?
Not important. http://gwt-code-reviews.appspot.com/1542804/ -- http://groups.google.com/group/Google-Web-Toolkit-Contributors
