[noam_k]

You might want to take a look at differential privacy. It takes an unintuitive amount of noise to make the system useless.

You also need to account for how "easy" it is to de-anonymize a profile.

(Sorry I don't have links to sources handy.)

[aleph_minus_one]

> You might want to take a look at differential privacy

Differential privacy is just a bait to make surveillance more socially acceptable and to have arguments to silence critics ("no need to worry about the dangers - we have differential privacy"). :-(