Upgrading Flex Viewer 3.0 to 3.1

Hi, I couldn't find a definitive answer to my question so I'm going to ask it here: I'm thinking about upgrading my ArcGIS Viewer for Flex application builder from 3.0 to 3.1. I'm currently using some of Robert's customized widgets. Will these widgets also need to be upgraded to their 3.1 versions or will his 3.0 widgets 'play nice' with FV 3.1?

Thanks