Enhancements to Web Parts in ASP.NET 4.0+?

Hi,
  We have been using Web Parts as of ASP.NET 3.5 SP1. We are wondering what specific enhancements are done (if at all) in Web Parts in ASP.NET 4.0 and beyond so that we can evaluate migrating. Is there somewhere a consolidated list? If so, I do not seem to find such a list on the MSDN.
In particular, does drag-and-drop of Web Parts in browsers besides IE can work without requiring AJAX futures?
Thanks in advance and regards