Just this week I read on one of those blogs I signed up for earlier about Microsoft offer this new Office-type software called Equipt, only cheaper. The article had this quote: "as much as we love free alternatives like OpenOffice.org, we have yet to find one that's 100% compatible with Microsoft Office" -- Brad Linder, ITLnet Blog. While Open Office is great and everyone can get it free, not everyone you send attachments too will be able to open them unless they go download it, too, and they just might not want to take up hard drive space with another program just to read your stuff. Since we have a license for Microsoft Office at school, I know we won't spend time downloading OpenOffice to every computer at school.
However, Microsoft Office's versions aren't always compatible with each other, either. Students will create something at home, save it on a flash drive and try to open it in our school's computer lab only to have it show up as jibberish because their version at home doesn't match the one we have at school. I always tell them to save documents in WordPad or Notepad, then they can copy and paste it into any wordprocessing document to edit/print when they get to school.