The server-side classpath is loaded from the war/WEB-INF/lib (with a fallback to the classpath of the DevMode, which prints a warning).
If you're using Maven, it's actually even easier to get your dependencies right there in the WEB-INF/lib: http://code.google.com/eclipse/docs/faq.html#gwt_with_maven (and follow the "If you're not able to use Eclipse for Java EE" rules, as you're not using Eclipse WTP in this case). -- http://groups.google.com/group/Google-Web-Toolkit-Contributors
