If you've been under a rock lately here's a link that'll show you the background to the Microsoft-Android patent battle.
One part of this that hasn't been clear is what patents are in play. Microsoft has been requiring all parties who have agreed to their licensing to sign Non-Disclosure Agreements.
Barnes and Nobles (you'll remember they're the maker of my beloved NOOK Color) has rejected Microsoft's patent claims and has published the details of what patents Microsoft is claiming that the NOOK's Android uses without licensing.
Note that I'm not endorsing the editorial position of Groklaw but rather just using their post as an anchor of the legal material from Barnes and Nobles.
For deeper background here're links to articles from Microsoft and Google's patent attorneys.
Regardless of your opinion/bias on this issue these are all interesting reading.