As far as I remember DoubleClick profile-based ad targeting business, in which the company invested huge amounts, fell when such targeting appeared to be ineffective. Instead, Behavioral Targeting seems to be promising, as I have read in Mircosoft China research report. Inspired by this report I am thinking about Discourse Targeting, at least in Social Media - please see my post http://discourseweb.wordpress.com/2009/10/12/discourse-targeting/
What do you think? Do you know other inspiring experiences and ideas?