Reviewers are likely to have a hard time shooting down the work of anyone they know personally, and in specialized sciences, the probability that a paper was written by a friend or former colleague of the reviewer is high enough to be a problem.

On the other hand, people have different, and often recognizable writing styles. If you're in a specialized science with a small enough circle, then you may be able to recognize a paper written by your friend (or your foe!) even though it was anonymized.

Or maybe you may even know that your friend (or foe?) is working on a paper on a specific topic just from reading their blog/Facebook/Twitter/etc.