In practical terms, Scoble is wrong: email doesn't enjoy the same protections as other communications like personal letters or phone calls. Technically speaking, most email is about as private as a post card; unless it's encrypted, anyone who encounters the message along the way can read it and repeat it. And once messages hit the inboxes of their recipients, it's really up to them what they do with it. Just like when someone shares some juicy gossip with you. Unless they say "don't tell anyone else," it's kind of up to you who else you share it with.
Scoble has the right idea, though: Ask permission first. Had Facebook only taken that simple step -- with changes it made last December to the information Facebook makes public by default, or the "instant personalization" features it rolled out in April -- it would have avoided the well-deserved pummeling it has received over the last few weeks.
The problem is not that Facebook shared that information. It's that Facebook didn't ask nicely first. And now it's going to regret its lack of manners.
Of course, some people believe that by sharing your information on Facebook you've given up any claim to keeping it private. They argue that, by definition, that information is already public. Well, yes and no. In truth, you've chosen to make that information selectively public. Some people know it, and some people don't.
That's the way privacy is supposed to work in the real world. It's selective by definition. The only things that are truly, purely private are the things only you know. Everything else ends up getting shared with someone -- whether it's your doctor, your lawyer, your spouse, or your 3,245 closest friends on Facebook. But that doesn't make that information less private.
Take the information you should never post on Facebook (or elsewhere) unless you want to be used as an ATM by identity thieves: Your Social Security Number, your date of birth, and your mother's maiden name. Everyone outside of LifeLock's Todd Davis would agree that these are stupid things to share online. Right?
However, if you want to apply for a job, pay your taxes, get health insurance, see your doctor, rent an apartment, or qualify for a credit card, you have to release this information. Does it make this information any less private? No. It's still your private information. You've just selected who gets to see it. (Though in this example, the Federal government and the credit bureaus made that selection for you.)