The ubiquitous Robert Scoble was kicked off Facebook temporarily for screen scraping his friends' email addresses via an alpha test program from Plaxo. Like almost everything Robert does, this incident reverberated around the Internet, with bloggers expounding on whether Facebook or Scoble were "in the right". In particular, here's Jeff Jarvis' take called In Defense of Facebook. You should also read Is There A Conflict Between Open Social Graphs And Your Privacy? by Julian Sanchez at TechDirt.
In my opinion, both Jarvis and Sanchez are making the same basic mistake, although Sanchez attempts to talk his way out of it. The real problem with Facebook's attempt to control the data flow, and Jarvis' and Sanchez' belief that they have a right to control the data flow, is that it breaks Russell's Law. Russell's Law (which I made up, but has been holding up very well so far) states: You cannot encrypt past the intended recipient. It was originally coined to convey the impossibility of enforcing "for-your-eyes-only" emails via cryptography, but it applies to many situations. Like the impossibility of foolproof DRM-protected music. Now, here's another situation where it applies perfectly. You can't stop your Facebook friends from giving your email address to whomever they choose. You can make it temporarily tedious, but that's it.