While TSA is in the spotlight on this, this is a problem common to many other agencies. The VA also recently lost a laptop that contained hundreds of thousands of personal data of veterans.
The problem is that we as a society haven't learned to get a firm grip on new technologies. On the one hand, it's great to have everything conveniently transmitted with the click of a mouse. On the other hand, there are people who can either intercept those transmissions and/or tap into networks to steal that information. In most cases, it's a simple matter of inadvertently sending information to the wrong person or not taking the proper steps to secure that information.
One of my military assignments involved working with computer network security. Once a quarter, we routinely waited for certain anticipated security breeches involving classified information transmitted over non-secure networks. The cause came from subordinate officers who prepared quarterly slide presentations that contained classified information which they would email to their superiors for review/approval without taking the necessary security precautions. In many instances, they would Cc several other offices as part of protocol or other routine interoffice coordination and staffing. Once a breech occurred, we had to "sanitize" several network systems; and if the breech was reported late, then the command had to go through the pains of resolving security compromises. Point here is that I see the same occurring probably with more frequency than we dare to imagine when it comes to personal data, especially SSNs, since they are routinely used for a multitude of identification purposes. While the focus of this article is on missing laptops, what's overlooked is the potential compromise coming from just a missing jump drive, especially those that hold 1-4 GB of information.