Add to this the ease with which anyone with a decent legal budget can get anyone else's personal data from the ISP in the U. S. of A., and contemplate the consequences:
http://digitalmusic.weblogsinc.com/2006/08/07/the-riaa-vs-john-doe-a-laypersons-guide-to-filesharing-lawsui/

"And these folks are telling me not to pick my nose!", as the bad kid (always having THAT on his mind) exclaimed in the classic Russian joke.

PS: Unfortunately, the original joke is impossible to translate because of several layers of cultural references, but the dear readers are welcome to invent English jokes with this punchline themselves.

AOL apologises over search data 'screw-up'
http://www.theregister.com/2006/08/08/aol_search_data_breach_apology/
AOL says privacy breach was a mistake
http://www.cnn.com/2006/TECH/internet/08/08/aol.search.privacy.ap/index.html
AOL: Breach of Privacy Was a Mistake
http://www.redorbit.com/news/technology/605686/aol_breach_of_privacy_was_a_mistake/index.html
One More Missing Computer with Military Vet Data (security breach)
http://www.dailytech.com/article.aspx?newsid=3708
AOL release of users' search histories called a privacy breach
http://seattlepi.nwsource.com/business/280395_aolprivacy08.html
AOL Data Spill Threatens AOLusers With Extinction
http://newsvac.newsforge.com/newsvac/06/08/07/2148204.shtml
AOL apologizes for exposing search data
http://searchsecurity.techtarget.com/originalContent/0,289142,sid14_gci1208972,00.html
AOL's disturbing glimpse into users' lives
http://news.com.com/AOLs+disturbing+glimpse+into+users+lives/2100-1030_3-6103098.html?tag=nefd.top
AOL's disturbing glimpse into users' lives
http://news.com.com/AOLs+disturbing+glimpse+into+users+lives/2100-1030_3-6103098.html?tag=nefd.lede
AOL Removes Search Data on Group of Web Users
http://www.nytimes.com/2006/08/08/business/media/08aol.html?hp&ex=1155096000&en=f8ca23c604bf5d54&ei=5094&partner=homepage

Copied from: http://catless.ncl.ac.uk/Risks/24.36.html#subj2

Greetings. I've written and spoken many times about the sensitivity of search engine query data. We all know about Google's stance in DOJ vs. Google early this year, where Google wisely attempted (for several reasons) to prevent release of such data to a government fishing expedition related to "child protection" legislation. We also know that Gonzales, et al. are merrily pushing mandated data retention laws -- again mainly in the name of child protection -- that would leave Internet users vulnerable to all manner of unreasonable surveillance of their Internet activities. All of this is already enough to be sounding alarm bells regarding the lack of reasonable legislated protections for such data.

The AOL action in releasing the search records of a reported 500K AOL users -- assuming it took place as outlined below -- is probably the most egregious violation of users' search privacy in the history of the Internet, despite the half-hearted attempt at crude anonymization. The unbelievable lack of responsibility or good judgment shown by AOL in this case should be enough to cause any remaining AOL subscribers (or users of their free services) to strongly consider ceasing any further contact with AOL.

Furthermore, we need to accept the fact that search query data is incredibly sensitive and often contains extremely personal data that does not lose its potential for abuse via simplistic forms of anonymization. Nor can we necessarily depend indefinitely on some individual search engines' honest and praiseworthy desires to protect such data (e.g. Google) in the face of intense competition and intrusive government actions.

Search query data can contain the sum total of our work, interests, associations, desires, dreams, fantasies, and even darkest fears.

We must demand that this data be protected.

--Lauren--