I’m under deadline pressure currently, so very quickly:
Declan McCullagh and Elinor Mills at CNet have surveyed the major search engine providers about their privacy practices related to retention of user data and behavioral targeting. Full story here, and the search engines’ actual replies here.
Excellent summary, but much remains unknown…
MichaelZimmer.org 
It was a good summary, but one thing I would have liked to see is some consideration for how protective search engines are with the data they collect. For example, if a search engine collects data to improve its searching algorithms but will fight tooth and nail to prevent it from being disclosed (e.g., by resisting subpoenas) then I’d be happier with that company than one which collects data and resells it to third parties.