So, the article at the top there is about selling advertising, which is a way to facilitate business people to communicate with their customers via Facebook. And you're suggesting that the idea of doctors communicating with their customers via Facebook is a ridiculous proposition which would have no application in the real world? Please come back when you're put a tad more thought into this, Anonymous Coward.
PS: I personally know at least two doctors treating chronically ill patients with whom they regularly communicate via Facebook. I might know more, but this is not a topic that I discuss with everyone I know. :) Normally, anecdote is not the sigular of data, but in this case I'm pretty sure that there has been "protected health information" recorded in Facebook's data centers.
Which bring up the question as to whether they're doing enough to comply with HIPAA laws. And PCI laws, as some bone head has probably sent credit card numbers through "private messages" at some point. With sufficient creativity, it'd probably be possible to shut Facebook down through regulatory compliance audits, unless their TOS is equally creative. ;)