I have great respect for Aaron's accomplishments and the depth of thought he brought to most problems, but his contribution to Open Government isn't his best work. In particular, its nearly-complete dismissal of transparency as a meaningful intervention suffers from a failure to consider likely counterfactuals. Transparency's impact is probably greatest through deterrence. It shifts equilibria. Aaron's view of it -- at least the one expressed in this chapter -- was ploddingly instrumentalist. Virtually any policy is going to be unsatisfying when viewed through that kind of lens.
I'll admit that my opinion on this is shaped by both personal and professional considerations, but I really do think that Aaron got this one wrong. More here, if anyone's interested: http://www.manifestdensity.net/2013/01/18/how-transparency-works/