Some useful sites for GWT, GAE, Maven + Eclipse:

• http://googlewebtoolkit.blogspot.com/2010/08/how-to-use-google-plugin-for-eclipse.html
• http://stackoverflow.com/questions/877949/conflicting-versions-of-datanucleus-enhancer-in-a-maven-google-app-engine-projec
• http://code.google.com/webtoolkit/doc/latest/tutorial/roo-sts.html