Do people still run screensavers? That's pretty irresponsible. The monitor should be turned off, and most of the box too.
But this is really about automatic time-out screen locking, and authentication. We're still at a very primitive stage there. Arguably the machine should give you library-PC features with no authentication, and then enable more features as it gains confidence that it's really you. Passwords would be just a way to speed that up. To recognize keyboard timing signatures would give enough security, by itself, for almost everything.