iTunes and Windows Media Player both assume, by default, that every user wants to have a private collection of music. Maybe when my son is 17 that will be the case, but now that he's 10, a shared pool is what we want. Neither of those programs makes managing a shared pool effortless.
Having to log out and log in (dump my son's game on the floor) so my wife can check email is just lame. (Switch users isn't much better)
Laptops today all come with cameras and face recognition technology is pretty good, so in a family situation the system should always know who's sitting in front of it.
And yeah, autocompletion on your web browser should NEVER turn up a porn site...