I use Office 2003, yet when I received an e-mail from our State Department of Education with an attachment saved in Word 2007, I had no problem opening it. Within an hour, however, I received another e-mail from the same person saying they had gotten complaints from people who for some reason could not open the attachment. The new e-mail simply included all of the information from the attachment pasted in the text of the e-mail message.
The very next day, I received an e-mail with a Word 2007 attachment from another person in the same department. You guessed it, within an hour, I was looking at a second e-mail, this time with the same attachment saved in Word 2003.
I can only imagine how many phone calls, e-mails, and people who became involved over something that we all need to deal with.
Since that post, Office 2007 has become more prevalent, and the information in that post is even more needed now than it was months ago.