Microsoft Outlook Express stores email files in a hidden data folder buried deep in the user's home folder. It makes it nearly impossible to selectively backup your data files unless you know exactly where it is. I can't tell you how many people have lost years worth of email because they didn't consider delving into this hidden directory.
While Microsoft won't win any usability awards anytime soon, this design is a booby trap. What possible reason is there for hiding incredibly valuable data from the usersuch information?