The May 2009 Release (build 188.8.131.523) is live: http://mfcmapi.codeplex.com.
The coolest new feature has to be the addition of Smart View parsing to the Hex Editor. I actually had the idea to do this the morning I published the March 2009 release, but didn’t want to delay that release any longer. One side effect of exposing the parsing in the Hex Editor is I was able to do much better testing of the existing parsing engine and fix a bunch of memory leaks and crashes.
Here's a change list - see the Issue Tracker on Codeplex for more details, or look at the code: