Joel Spolsky has an excellent deduction of user interface complexity on line.  Windows Vista (and XP, and most Linuxen) have a myriad ways of logging off, shutting down or just getting the heck out of the session. The Vista equivalent of the Start menu has buttons to lock the session and to shut down the computer, as well as an additional menu to power off, lock session, sleep, hibernate, restart and switch user.  In addition to this, most modern computers — laptops in particular — have buttons or FN-combinations to sleep or hibernate (and which normal user actually knows the difference between “sleep” and “hibernate” modes?), and some to log off or power off.  Oh, and you can configure the laptop to do any of those actions by closing its lid.

Choices lead to confusion, confusion to pain and pain to headaches and frustrated users.  Spolsky on the other hand shows that you can deduce the above fifteen choices into one.

Not bad.