I found an interesting thread about GoogleSharing where one user hints at the following:

---QUOTE---
So, let's say some other user using this service searches for something illegal (I'm sure you can think of something they might search for, and not only that, but these people will gravitate to such a service because of the supposed anonymity it offers), and let's say that this gets an ID from the service, then when I search this ID is now passed to me (by chance). Does this mean that when they track it back that there is a possibility that somehow I will be implicated in legal problems because of this?

GoogleSharing:

Two people make a search:

me: something not illegal
other: something illegal

The way Google sees it if, by chance, GoogleSharing mixed the identities this way:

me: something illegal
other: something not illegal

OH NO!!!

---END OF QUOTE---

As the thread endet without an answer to that question, I'd be interested in knowing what you think about this problem.