Thinking about it, I like Helmuth's idea of tag clouds for contacts, if you can also use those tag clouds as a way of controlling when you get alerted - for example tagging a period in the calendar so that only contacts with a 'family' tag will make the call ring.

The one problem with that is that if (as I do) you want certain times every day limited to family callers, then you probably need a 'profile' or some other screen to set those, otherwise the calendar might potentially get crowded with entries that do nothing other than control what calls you get.

It would, though, be useful to be able to add multiple options to contacts, so there could be some clients I am happy to hear from outside office hours, but still have the 'work' ringtone, so I know when I hear it that it's not going to be friends or family, and I can act sober when I answer.