My friend Mike White told me the other day that he uses the photo sharing service Instagram because it makes him happy. That stuck in my head.
It says nothing about the product or service, but says everything about the way they want you to feel after using the service. If you didn't know what the Cheezburgers were all about, you can imagine any number of things they might deliver to give you those 5 minutes of happiness.
I use Wordnik all the time. Not because I am looking for word definitions (though it delivers that), but instead simply to look at words. Their mission: "Wordnik is all the words, and everything about them." Again, nothing really about the specific product functionality. I have a list over there called "Good mouth feel words" - words that sound nice when saying them.
Turntable.fm is also a daily stop for me, particularly the Folk/Americana/Blues/Soul-It's All Connected room. That service's theme: "we believe music is better with friends." Music. Better. Friends.
Defining services around a grand theme or even emotion allows them more flexibility to deliver interestingness (noun: "the power of attracting or holding one's attention because it is unusual or exciting etc.) and over time iterate on that delivery - how it might evolve. Flexibility should be a hallmark of an evolving business.
But defining a service thematically should also provide more opportunities for new, native business models to emerge from their usage. You can't slap magazine style advertisements on these services and expect them to work - for the user or the advertiser. I bet however that business models centered around "themes" - whatever they may be - will work.