Generate a new project with
===
project --topLevelPackage com.ma.hi
//persistence setup --provider DATANUCLEUS --database HYPERSONIC_PERSISTENT
persistence setup --provider DATANUCLEUS --database GOOGLE_APP_ENGINE

//data model
entity --class ~.server.domain.Person
field string --fieldName firstName
field string --fieldName lastName
field date --fieldName birthDay --type java.util.Date

entity --class ~.server.domain.Address
field string --fieldName street
field string --fieldName zip
field string --fieldName city

entity --class ~.server.domain.Country
field string --fieldName isoCode
field string --fieldName name

gwt setup
quit
===

According to http://jira.springframework.org/browse/ROO-544 , from Eclipse do Import -> Maven -> Existing Maven Projects.

Right click on project -> Google -> Web Toolkit settings. Use Web Toolkit checkbox is off, should have been on. Same for project -> Google -> App Engine settings

Other issues, should I report more bugs?
1. AddressDetailsViewBinder.java has error AddressDetailsViewBinder.ui.xml is missing (indeed, only AddressDetailsView.ui.xml is present)
2. Project -> Run As -> Web Application will give "Could not find any host pages in project:". The fix listed at http://forum.springsource.org/showthread.php?t=89612 didn't work, as Maven was already managing dependencies.

Thanks