I'm too lazy to come up with a title
I agree that Office XML is too complicated and absolutely hated the fact that it did get approved as a standard in that sham of a process. I've not seen any of the files produced from Office 2008 SP2 on Mac or know how it handles them, but what I wonder is if the problems could be rising up from the fact that Office 2007, at least in RTM and SP1, don't use the ISO-approved standard Office XML, which changed a lot from the original implementation.
That said, it's a horrific shame that OpenOffice.org, the leading proponent of OpenDocument Format (which I do endorse, mind), didn't even support antialiasing its rendered graphics until the latest version, version 3.1, and also lacked hardware graphics acceleration until fairly recently as well.
All that said, Microsoft Office 2007 Service Pack 2 for Windows XP/Vista/7 supports ODF 1.1 natively without additional filters, as will Microsoft Office 2010 upon release. Even Wordpad in Windows 7 supports .odt files. Too bad ODF 1.2 is the current version of the format in use elsewhere.