OASIS Open Document Standard
Open Document standards are such a good thing for so many reasons. The world would literally be a better place without proprietary document formats (especially Microsoft's because they seem to go out of their way to make their document formats incompatible and difficult to work with).
I think that one "killer application" of open document formats will be web based content management systems. Last year I designed and wrote a web based CMS system and dealing with Microsoft Document formats was a pain until my customer licensed dtSearch which handles a variety of document formats. For "rolling your own" support for handling a variety of document formats, see my DevX article last month on Lucene that included support for indexing and searching Microsoft, OpenOffice.org, AbiWord, etc. I also have support for this in my KBtextmaster open source project.