The GWT team just released the RC1 version of GWT. The 2.5.1 is merely a maintenance release, and the list of bug fixes can be reviewed here:
https://developers.google.com/web-toolkit/release-notes#Release_Notes_Current
The release candidate can be downloaded from the link below, and is not availabe in the maven central repository (yet?).
http://code.google.com/p/google-web-toolkit/downloads/detail?name=gwt-2.5.1-rc1.zip

