If you want to share data, browsing history, etc. I don't have an issue with that. However, I don't think a lot of users actually understand what is going on with their data. These companies have difficult to understand user agreements, update them on a semi-regular basis, and it is difficult (or impossible) for someone that isn't clairvoyant to understand what is going on with their information. Also, they see this type of stuff all the time and it has become habit just to click through it since they will need a lawyer to decipher it anyway.