Matt Gemmell, on the subject of social apps uploading raw user data instead of hashing the data:

From talking to many developers about this privacy intrusion during the past week, it quickly became disturbingly clear to me that many aren’t familiar with hashing at all. This is also predictably (and entirely forgivably) true for the many journalists who have covered the story, unintentionally distorting the issue due to lack of education in the field. This article, therefore, aims to introduce the concept of hashing in a clear, straightforward, and no-degree-required way, suitable for journalists and casual readers as well as programmers and software engineers. I’ll also explain why it’s suitable for preserving the privacy of contact information whilst still allowing for social functionality, and I’ll touch on whether or not you really need to store that contact information (hashed or not) in the first place. He goes on to outline the things he touched on in the paragraph above. This is a must-read article for any web or app developer.