Leveranging the human physical assets, the mobility and geographical placement by using personal space wireless tehnologies for delevering context targeted rich content ;)
First premise: the over-population and the people’s need of reshaping their surrounding social space. That’s why iPods are so popular.
Second premise: the excess of socialization options and the need of a selection system
A hitech solution for these two: something based on bluetooth or wifi, integrated in iPod and that broadcasts what its owner listens. Plus additional information – exactly as a personal portable portal. Resumes, classifieds, pictures, blogs, contact cards etc. With a selection and admittance system based on different users types: strangers, casual acquaintances, pals, friends, relatives. The next-generation MySpace.com.
What’s the utility? First of all it’s socialization. You accost easier somebody who is listening to the same type of music as you listen. There are common background odds.
Moreover, the possibility to promote your classified ads: I sell roller skates. I realized that I prefer cycling. This for example for those environments where interests convert. For example a bikers’ club, where specialized cycling ads blow up publicly. Of course you can also imagine a sort of an automatic stock exchange.
Or advertising through inserts of content emissions. A pretty girl in a crowded area could make nice money. 
Or an efficient signaling form taking into account the erosion of marriage as an institution and the disappearance of “I’m taken” symbol of the wedding ring. And these being caused by the growth of concubinage.
Like RFID on steroids. Speaking of RFID and of point of sale, I think that some products that could tell their story to the client would be really cool for the market leaders. Especially if these products incorporate a real informational component.
And, exactly as signaling, here is something I am thinking of: The digital cryptographic brands/labels. Something based on PGP or on another crypting method that contains and broadcasts digital signatures of the used brands (in order to reduce to 0 the chances of producing imitations).
I really think that these things aren’t an utopia. The future is rich info placed in the acquisition, contact or consumption point. Every time you’ll see these gizmos on the street, remember that here is where you read about them for the first time.
PS1 The academic title is for fun, of course.
PS2 If web 2.0 is about meshes on existing applications, API’s and the access to the external databases, web 3.0 will become web 2.0 plus the omnipresence of the information, full mobility, all kinds of various small gadgets that talk between them and the confusion between online and offline.