This is a pretty cool deal; nice to see an open-source powered company that has found a self-supporting niche.
It will be interesting to see how they strike a balance between making money and keeping things (like Mono.Mac, MonoDevelop, etc.) open... and if they are able to build a community of outside contributors around the open-source parts of their solution(s).
It would be nice to see a blog post or two on the mile-high long-term etc. goals Xamarin has for the open source aspects of their tech... or perhaps a pointer to any existing summary. As you've pointed out, Xamarin is rather quietly contributing a lot; it would be great to have a place to point the non-developers to that explained this as well.
It will be interesting to see how they strike a balance between making money and keeping things (like Mono.Mac, MonoDevelop, etc.) open... and if they are able to build a community of outside contributors around the open-source parts of their solution(s).