The general impetus toward information-sharing among government entities and the massive investment in technical solutions may eventually deliver to the government the ability to process data efficiently. Finally, the rate at which individuals shed transactional data simply by living in a networked world seems to increase daily. The composite picture of individual activity that can emerge from such data is often of startling clarity, and will likely sharpen with in the future.

We don’t really have a coherent legal theory to address appropriately the growing privacy interests in this kind of data. The full-scale judicial supervision accorded electronic surveillance and physical searches is probably overkill, and far too cumbersome for data for which basic investigative access is justified. On the other hand, the Miller view that the "consensual" delivery of this data to third parties strips it of any privacy interest looks untenable when one considers the effect of the information aggregated.

There are some good comments on the National Security Letter situation in this post at The Volokh Conspiracy. I've been meaning to comment on this at length, but it's not going to happen any time soon. I have some reading I need to do. I'm not nearly as familiar with the justices' opinions in United States vs. Miller as I would like to be. I've been meaning for awhile now to sit down with a cup of coffee, read, and fully digest that case.

The Volokh Conspiracy - More on National Security Letters