Craig,
I'm not sure. I have two legacy iOS apps in the store, and I had to get Xamarin just to keep them running. (Thanks to them for giving it to me free.)
I think that I had trouble with the latest Catnap on the latest MonoTouch, but I can't exactly remember for sure. I do believe that the terse version of the mapping was not working, and I had to go back to the long version. MonoTouch definitely has recurring troubles with regressing when it comes to heavy generics and lambdas.
Tim