A common profile just for iOS and Android libraries (not pcl)
The PCL path is nice and I think that it must be the path to go, but even if xamarin supports it 100%, there are parts of the .net legacy that you can't reach with it. I mean, you cold use it on ios or android but you can't use it on a share project. Of course you can compile and get the dll, but I'm talking about a "project level".
It should be easy to get a profile just for ios and android, this way people who are getting started can use their .net legacy knowledge to build cross platform apps (like it or not, WP is a secundary target) and not just apps for ios or android (linking files can be a mess).