I think that privacy and control will be big issues in digital marketing this year, so it's interesting to see that Google are now offering an explicity opt-out from cookies set either by Google or by their adserving network Doubleclick. This button is very prominently displayed on Google's main page about Advertising and Privacy.
This is a really encouraging development. Without services like this, consumers trying to protect their personal privacy are often forced to delete all their cookies - which will also remove saved settings on many websites, like login information.
Rooting around, it turns out that this service is being run on behalf of Google by the Network Advertising Initiative, which offers consumers a route to opt out of a whole host of advertising networks including Advertising.com, Yahoo and Atlas.
Of the 17 networks listed, I have active cookies from 9 (not that I am particularly obsessed with deleting cookies - working for a media agency, that would be a tad hypocritical of me!).
The opt out page for the Network Advertising Initiative sits at http://networkadvertising.org/managing/opt_out.asp.