Sort of sideways, but this is an interesting thread and I thought of it here so...
UP strikes me, honestly, as a parenting method. A relatively cool one (I really do have reservations about the authoritarian trump card which seems to me to be a big flaw in it both theoretically and practically), but a method just as much as the whole supernanny thing is a method.
And, as people are already saying on this thread, any method is only as useful as the people involved in its implementation allow it to be - and children don't necessarily know that they are supposed to be routine children or supernanny children or UP children or whatever else it is.
I think philosophy is more important. We all have parenting philosophies, lots of them are unconscious or semi-conscious, but we all have a basic philosophy on how family interactions should look, how any power politics should look, whatever. However we are treating our children, whether it is rewards and punishment or UP or whatever, we need, for our own sakes, to be completely comfortable with who we are and how we are around our children. Otherwise it's just guilt and tension and internal inconsistency.
Parenting philosophies I like, which UP seems to me to be a bit of a watered down method based on, include:
Taking Children Seriously (oh yeah, Karl Popper's theory of knowledge applied to family life by people including one of the world's largest brains [David Deutsch - theoretical physicist] - what's not to like?!),
the Jan Hunt Natural Child project,
the Kabatt-Zinn Mindful Parenting approach (although I'm a bit allergic to the yoga-for-10-hours-a-day-and-I'm-a-perfect-Dad father - it's the zen approach I like),
the Radical Unschooling movement,
and I'm hearing very very good things about Naomi Aldort "Raising our children, Raising ourselves", and I like the acknowledgement to Eckhart Tolle in the preface - all stuff about living fully in the present, but I haven't done more than dip into it yet.
Gawd, what a homily.