I was sure that Amazon had acquired broad patent licensing from Microsoft vis-a-vis their use of Linux in general, but interestingly those licenses apparently DO NOT cover Android [1], which of course includes the Kindle Fire. it will be interesting to see how that turns out, but I would guess that if they already licensed X they'll be much more amenable to licensing Y from MS.

[1] http://www.electronista.com/articles/11/09/30/kindle.fire.is...