Hi,
one of our customers has great problems checking in documents to a SharePoint library form Word 2007. Whenever she check's in a document to the library the meta data as version number and checkin comment are updated but not the document itself.
The library is configured in such a way that versioning is activated and documents have to be checked out before editing.
I think it has to do with some Office 2007 or OS settings as every other of her colleges can check in documents without any problems.