In the US, M$ can sue you for USING their patents w/o permission - no matter whose hard work it was to infringe them.

However, it ain't gonna happen.
1. 50% of US patents are invalidated in court. This number is probably gonna be even higher with software, since there have been much shenangains (one-click, not operator, etc.) and the 50% figure includes the traditional, stable fields of patent law (ie. pharmaceuticals). Ask Amazon, who knows their one-click patent is junk and settles for favorable terms rather than see it invalidated in court.
2. Unlike copyright, there is no criminal remedy, and no mandatory damage assessment. M$ would have to prove almost every penny you cost them. (most likely $200 or whatever the hell a copy of Word goes for these days). (Other damages are available but not common) Which leads us to...
3. Patent Litgation is EXTREMELY expensive. We're talking millions. It's not worth M$ cash to go after you.
4. Multiple defendants can fire all the bullets they want at the patent. Only one has to hit - one judgment of invalidity, and bye-bye patent.

Not to say that this is not worth concern, they might target OO.org itself, or a large company with the $$ to supprt a judgement, and the result may very well affect how we use OO, but you're not gonna get hauled into court over it.

If I remember correctly, MS stole the idea of a desktop environment (with icons, trash can, etc.) from Apple, who in turn stole the idea from research at Xerox PARC.

That's just how it goes in this industry... Deal with it!
Enough with the patent nonsense already

anyway, has anyone been sued by MS because of using their formats under OO.org?

That doesn't make any sense. It doesn't matter what the licenses do. The only way that M$ can pursue the end users is with an injunction based upon patent law. If M$ starts suing end users of open source software, count on open source foundations getting behind the users and counter-suing to invalidate the patents based on prior art, etc. Most patents issues in terms of software will fail as a result of prior art... others will fail based upon collateral estoppel.

A license doesn't need to bring liability back onto the developer. There have been a lot of false claims with regard to what a software company can do with regards to suing end users... Just because an open source license claims no liability on the part of the developer or distributor, do not think that the end user ends up holding the bag...

My Coke analogy holds true. M$'s ability to go after end users of OpenOffice is extrememly limited, even if their Word patents were validated (but probably won't be).

Before you think I am talking out of my anal spincter, I am a lawyer, not currently practicing, and not with an IP background, but I do know a thing or two more than a lay person about the law.