Let me guess, you're a philosophy major?
It is an interesting article, but there happens to be many assumptions based on a lot of "ifs" and maybes".
BANs, wireless sensor networks.. would the general public ever allow this to happen on a large scale?
Furthermore, the article mentions the infrastructure for internet itself. It looks like the potential "compute resource" will far exceed what can be transfered over our current inrastructure that exists as is.. I mean, how can global applications exist if we don't have the infrastructure to support such vasts amounts of exchanging of data? There are few countries that are creating the infrastructures needed to allow for this type of theory to exist. It advocates a system where people dedicate resources to a pool that could be tapped, but would this be viable? it would have to be entirely collective that would require vast amounts of global cooperation. Same goes for the creation of such interconnected "grids".
You would almost need to "socialize" per se, all of the world's datacentres and remove all the barriers to allow this to happen. Ie. allow free and unrestricted access to servers so that applications could run freely and make use of the potential reserves of resources that exist. Would that be able to happen? will the internet "castles" lower their gates and let us in for free? who knows.
It's an interesting theory nonetheless, but from a political perspective, there are many boundaries that exist that I think would prohibit the creation of such a global "ambient cloud". The cloud would literally have to transcend political boundaries and differing jurisdictions to be able to exist and I question whether or not that that's even possible, although we are already seeing this happen with large virtual networks such as the folding@home network I suppose...
That's my take anyways.