I used to spend a lot of time in my younger years reading and scribbling down quotes that pleased me in various dog-eared ex-exercise books. One of my favourite sources was William Blake and, along with that thing about "the road of excess", one of favourite quotations was from "The Marriage of Heaven and Hell":
"Without Contraries is no progression. Attraction and Repulsion, Reason and Energy, Love and Hate, are necessary to Human existence."
Brands that are worth their salt (and worth progressing) seem to know this. The best brands satisfy two (seemingly) conflicting human needs or desires simultaneously. In the days when I worked on P&G, just about every brand I worked on from Oil of Ulay to Ariel was about effectiveness on the one hand and care on the other. And who hasn't ever worked on a food or drink brand that has tried to deliver "health" and "taste" (and has any yet succeeded?).
Most of the "new" brands these days seem to be about the Contraries of Individuality and Belonging. iPod is probably the best example, but amazon, MySpace and Facebook are also in there.
It's a simple principle, but I think that it's much easier to develop interesting communications for a brand with inherent tension than for some uni dimensional onion.