Blog in Dm tracks the sale of his personal information. He advertised in a local Jewish advertising publication where his name was mispelled, allowing him to track the movement of his mailing address information. Quite an eye-opener: link
Dr. Asher Meir discusses this in his latest The Jewish Ethicist column (link):
The Talmud makes the following inference from a Biblical verse:That's regarding a charity. But I'm not sure that there is any halakhic permission for a periodical to sell the information of one of its advertisers.What is the meaning of the verse (Proverbs 27:14), "Who blesses his fellow in a loud voice early in the morning, it is considered as a curse"? For example, someone who is taken in as a guest and treated well, the next day he goes out to the marketplace and proclaims, God bless so-and-so who so exerted himself on my behalf, then people will hear and pressure him. (1)Revealing someone's private information, in this case that he is a soft-hearted host to strangers, can be a curse since it exposes him to unwanted pressure from other prospective guests, some of whom will not be particularly needy. People are not always thrilled to be praised for their willingness to help strangers. [See also Bava Metzi'a 23b - GS]
However, the recent authority Rabbi Moshe Feinstein writes that since giving charity is an obligatory mitzvah (commandment), it is always permissible to tell a worthy recipient that a particular person is likely to help them out. The reason is that soliciting charity in a non-pressuring fashion is doing someone a favor, since it gives them an opportunity to fulfill the obligation to give charity. The exception is when the donor explicitly conditions to make his generosity anonymous. (2)
1) Babylonian Talmud Archin 16a and Rashi's commentary.
(2) Responsa Igrot Moshe Yoreh Deah III:95.