As this thread shows, there seems to be an issue getting JSPs to compile in GWT hosted mode with the new Jetty server:
2. ERROR in /tmp/Jetty_0_0_0_0_8080_war___
This problem is generated by the default values used by JspServlet, which compiles using 1.4 for source/target values.
You can cofigure this servlet by adding
jsp
org.apache.jasper.servlet.JspServlet
compilerSourceVM
1.5
compilerTargetVM
1.5
3
I described the solution at http://code.google.com/p/raisercostin/wiki/GwtEclipsePluginDebug too.