Everytime a preview, alpha, beta, and final release of KOffice is announced, this question would arise: OpenOffice.org can handle Microsoft Office files pretty well. Why doesn't KOffice reuse the code? Especially since default file format KOffice 1.5 is OpenDocument Format (ODF), just like OpenOffice.org 2.
Answer: the code for OO.o converters is tightly integrated with the rest of OO.o. It will take a lot of effort to pull the relevant part and place it in a library so that KOffice can also use it.
If somebody is willing to do it, of course we'll happy to consider it.
That does not mean that there's no cooperation. Look at libwpd, a library to read WordPerfect document (or WPD files). OpenOffice.org, Abiword and KOffice are all using this library already to import *.WPD, isn't it great? In this case, it is easier because previous OpenOffice.org did not have support for WordPerfect import and thus a clean library could be designed with code-sharing objective in mind.