If you're looking to avoid disclosing personal data, then it's a positive. On the other hand, if you're actually making use of a service, then it would probably lead to a lot of unwanted targeted information. Then, assuming a future of ambient intelligence where most people don't question machine mined data (I'd say an inevitability), you'd probably have a lot of awkward moments ensue, especially if public and private institutions hold data to be sacrosanct.