I'm expecting this to be common course for software companies in the near future.
More information on patent defense insurance:
Th X-Plane case, however, is what I think most people on HN tend to be worried about. An entity coming at you with an obviously invalid patent, and going for volume: hoping to get a few hundred people to pay a few thousand in fees each hoping nobody will litigate. It doesn't cost anywhere near $50k to throw a quick, cut-and-paste lawsuit together.
I'm sure you meant that hypothetically, but in case you are not aware:
Bill Gates personally, and probably Microsoft as well, are investors in IV - and best friends with IV founder Nathan Myrvhold - who quit Microsoft to start IV.