I spend a few hours getting the latest version of Eclipse, Maven GWT Codehaus plugin, and Ext working together, on both command line and via Eclipse.

The version I used follows, but this should work with any of the latest versions.

Eclipse: Helios
M2Eclipse (latest version)
GWT Plugin for Eclipse (latest version)

org.codehaus.mojo gwt-maven-plugin: 2.2.0
com.google.gwt maven plugin: 2.3.0

Full How-Tos and documentation can be found here:

Good luck