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Yep I got bit by that one, funny thing is I was using Office 2003 at the time and they were using Office XP (no I didn't *want* to use 2003 but that was what they had on some of the systems at the time). Different versions of office don't always treat their own files the same, so that's an issue bigger than simply Openoffice's word compatibility. And don't even get me started on opening Office 2000-created files in 2007, that can be worse than OO in some cases, much worse. Same for office on the PC vs on the Mac, it can be a nightmare.
The thing is, even with a so-called standard document format, people have different ideas of what some of the features mean and how they behave. So I'm not sure we'll ever have 100% compatibility across office suites even with the same file formats. And then there's those that ignore the standard or deliberately use it differently to "add features."