Facebook is at a very challenging point right now: they need strong short-term PR, very fast patching up of issues as they arise, cleaning out the tech debt they acquired in their youth, and most importantly, battling off the fierce competitors of all stripes and colors: from Google to Twitter to foursquare. Will they be able to do it? Based mostly on their ability to capture as large a market as they did and their fast attention to issues as they arise, I think so: as long as they don't piss off their users enough for them to leave en masse (and they haven't - most of their users don't care about the privacy issues we go crazy over), they just need to hold on and keep doing more or less what they've been doing.
This sounds like by far the most likely explanation for most of the Facebook problems. The Facebook non-system has become sufficiently internally complicated that no one person understands it anymore, which makes it easy to overlook security weaknesses. The systematic attempts to "share" information on the part of Facebook's leadership have been quite annoying, and have made me MUCH more circumspect in my Facebook behavior, but all the rest of this is just sheer inadvertence.
When the world's second largest site allows you to monitor the private chats of 400 million people - when it leaks your IP address to other people via e-mail for no reason - and now when it's leaking people's e-mail, then it's a big deal.
That's not even taking into consideration the privacy issues that were not bugs.
I still have these mails in my inbox. People who I've never met nor conversed with online in my life.
And whether it's sensitive depends on the context. Revealing one's IP reveals their location, and I can think of many cases in which this is sensitive information.
Unless someone knows exactly how the internet works, getting their IP address via social engineering is trivial. Facebook's behavior was not a big deal, though fixing it was a positive thing.
This is an actual privacy bug.