Given that it's presently possible to offload data processing to a number of cloud-based computing services, I'm not sure that we should be afraid of the comput

Given that it's presently possible to offload data processing to a number of cloud-based computing services, I'm not sure that we should be afraid of the computation cost. If you are willing to make some assumptions about independence (for example) you can do a lot of the computations in parallel. A more subtle issue would be how much the use of social net data would gain Amazon or Netflix over their current recommendation engines. I suspect it would be quite a lot, but that's just a guess.