The one possible privacy problem that I can see is that they are selling tweets that users can no longer control - if I said something a year ago that I wish I could take back ("Hi everyone, just to let you know I'm gay" or whatever), I'm now unable to delete it, or even review what it was I said, but it can still be sold and tied to me.

Still, not something I personally have an issue with, and I suspect not something most people would have an issue with.

Agreed. I use twitter as my public micro-blogging/rating/raving platform, and for them to sell data that I assumed was already being pulled by anyone via the API is a non issue to me.

The people who are shocked and offended don't understand that they aren't the user of these "free" social networks (Twitter, Facebook, LinkedIn, etc). They / we are in fact the product and once it's realized that your data is being sold to others than you will change the way you interact with the networks.

so true. public is public. Anyone could have data mined all these twitts... But the difficult question that may rise is the "right to delete". IMO it's a hard dilemma: history VS privacy. Can someone decide to delete all its trace and destroy everything he built? On the other hand, we need to keep trace of what's happened in the past, don't you think?