MvvmCross was perhaps a bit late to the fragment game - but with v3 we introduced full SupportFragmentManager library support and got them up and running with samples like:
However, one are these samples don't cover is how to use fragments in a generic way for navigation within MvvmCross' ShowViewModel mechanisms.
Take the stage @opcode - with an awesome blog post and sample code on how to do exactly that.
If you're using fagments and want to navigate by them, then check out: http://enginecore.blogspot.co.uk/2013/06/more-dynamic-android-fragments-with.html
100% awesome and very well deserving of a badge - awesome!