Provided the widgetset can be extended (see linked story):

• We use a new "aggregating" widgetset at bundle level, and only GWT:compile there
• We use a pattern that works for third party developers, and that they can reuse
• We split the whole widgetset out of ui/bundle projects so that it's sensitive only to client-side changes
  • no more gwt compilation in ui, giving some relief to internal developers and hopefully hudson too
• We try to get rid of dependencies from widgets to vaadin-integration, api

Details at http://wiki.magnolia-cms.com/display/DEV/Widgetset+and+browser+support