Stop the pseudoneutral and fanboyish arguing?
People are making some valid points here but they're getting lost admidst the rest of the comment that they're in because the writers are getting over zealous in their opinions.
Also several points are being made without and justification or reason, and some are just plain wrong.
For one, OpenOffice can and does open .doc and .xls files quite happily in its respective applications. The only issue with .doc files is that occasionally if some of the more unusual graphical options have been used when creating the document with MS office, the layout won't be 100% perfect, but if that happens it can be fixed in all of 5 seconds by moving the graphic slightly etc.
It also takes only about 5 seconds to change the preferences in OpenOffice so that its default file types for word processing for both opening and saving documents is in fact the 'Microsoft Word 97-2003 .doc' standard. Documents saved in .doc format using OpenOffice will open perfectly well in MS Office, and its my suspicion (and it is that, i have no evidence for this) that the reason some MS .doc files don't layout properly in OpenOffice is because MS don't actually conform to their own standards for .doc files fully. (just a side note that OpenOffice has built in, for free, the ability to export your documents as PDF files, which MS Office does not. Advantage to OpenOffice in format support there.)
To clarify the point about OpenOffice running more slowly. This is not the case, but it CAN be. Both MS Office 97 - 2007 and OpenOffice have a quick loader facility, where-by the core of the software package is loaded when Windows starts up so that when you open a document the application takes less time to load. The difference is, depending on the revision of OpenOffice, it is not always enabled by default, but again this can be done easily. The reasoning behind having it off by default is to save system resources and allow faster system start up.
As far as user interfaces go.Personally i do prefer MS Office, it would be hard to argue that MS Office does not have a more polished user interface that looks prettier and can more comfortable to use for some things. However OpenOffice has a perfectly functional user interface that does everything that is required without distractions which can be preferable in some instances, I'm writing my University Dissertation in OpenOffice because I find easier to concentrate without the distraction of help tips and huge array of buttons and features in MS Office.