One thing that irked me about both common Cairngorm practices and early MG:Flex "autoproxies" is the use of the controller tier as the responder for async calls.  Model-Glue: Flex solves this by using a combination of business delegates and messaging.  <a href="http://www.firemoss.com/blog/index.cfm?mode=entry&entry=6D96F27D-3048-55C9-436725DC9CEF7549">Read the full article at firemoss.com</a>.