Deleting a user will nuke the account itself, and assign all content owned by that account to an anonymous/deleted account.
The context is preserved and no-one else's data is affected, but we've removed all Googleable trace of the original account (the username and profile).
The only remaining issue is whether a person made posts containing personal information (defined as being the same as personal data according to EU Data Protection laws... name, phone number, email, etc). But for that we'll always honour take-down requests even when the information is orphaned from an ownership record.
PS: To the downvoters, I'd love to understand what part is objectionable.
I didn't downvote you before, but just did it now.I automatically downvote all comments complaining about downvotes unless the discussion topic is about downvoting and upvoting. I just think that it dilutes discussion.
http://en.wikipedia.org/wiki/AOL_search_data_leak#Notable_us...
Both marked deleted means that specific post has been deleted (but not the user account).