I usally don't post links here but I always wanted to describe here how to extend the Eclipse Memory Analyzer. Since there's now a Slide Deck available that describes briefly how it can be done at
http://www.slideshare.net/AJohnson1/extending-eclipse-memory-analyzer it's not that urgent anymore to post a description here ;-)
I believe there's a huge potential in extending MAT for specific use cases, such as Android, Jruby, Scala etc.