Microsoft Word patent issue not a problem for Open Source
The i4i XML patent issue that could take Microsoft Word from store shelves, isn't a big problem for open source users in my opinion - for a very simple reason.
As far as I can tell, i4i is not a patent troll. That is, they are a vendor that developed a technology that they were using in their own products that were being sold. Microsoft was aware of them and they even had some kind of partnership which ended when Word 2003 was released including the XML features.
Whether an open source vendor uses the same technology somehow or not, isn't likely an issue in my opinion - since this is a case where the patent case is specifically targeted against a vendor with whom the patent holder had some kind of relationship.
Microsoft in my opinion doesn't quite have that same luxury, since they've been aware of this issue for several years. I suspect, that much as they did with EOLAS years ago, Microsoft will end up paying something and doing some adjustment too.
Open source users likely have nothing to worry about, but I do hope that project owners are evaluating their own code to ensure that they aren't now knowingly infringing on someone else's patent.