An interesting problem about 3rd party cookies is this: Google offers users to control their privacy settings using the Ad Preferences Manager (http://www.google.com/ads/preferences/). Now if a user has 3rd party cookies disabled, Google does not know the user, and thus cannot apply her preferences.
An alternative solution on the browser side (and I think I saw this before somewhere) would be to only send cookies to a 3rd part site if the user has visited that site 1st party style before; i.e. don't accept 3rd party cookies if they are new. That's a pretty weak signal in the case of Google (who doesn't visit that page?), but at least for many other websites it could improve the status quo ante. If I've never visited some ad network's site, they should probably not be able to track me. Ads could then display inline a "Customize Ads" link that allows users to opt in to targeted advertisement.
"User has visited 3rd party host somewhen" is probably too bad a signal. We'd need something like "User wants to use 3rd party website". That's probably not possible to build with the tools we currently have.
An alternative solution on the browser side (and I think I saw this before somewhere) would be to only send cookies to a 3rd part site if the user has visited that site 1st party style before; i.e. don't accept 3rd party cookies if they are new. That's a pretty weak signal in the case of Google (who doesn't visit that page?), but at least for many other websites it could improve the status quo ante. If I've never visited some ad network's site, they should probably not be able to track me. Ads could then display inline a "Customize Ads" link that allows users to opt in to targeted advertisement.
"User has visited 3rd party host somewhen" is probably too bad a signal. We'd need something like "User wants to use 3rd party website". That's probably not possible to build with the tools we currently have.