I unavoidably needed support for MS's .docx et al formats at work. I'd been more-or-less keeping up with Ubuntu and there was one upgrade where the provided OO.o had considerably better support for .docx et al. I thought nothing of it, but then stumbled across people lamenting OO's poor support... and very shortly afterwards happened to notice that the version of OpenOffice in Ubuntu quietly had a big Canonical patch on it. I don't know any other details, but I have not had any problems any of MS's ....x formats. There's a massive spreadsheet I update about once a month - and the dozen people who read it have no idea I save it with OO. :-)
(I just wish MS had decent support for ODF so I can give those out.)
Wade.