Some food for thought about ad targeting:
I'm vising MissionLocal.org, which is a local website about events/food/news in the Mission district in San Francisco, from Seattle. Groupon shows me a Seattle ad.
In this case, should the ad have been targeted based on where I'm coming from, or based on the page context, given the strong location signal present in the context?
Targeting systems do wrong in not considering geo-location as a signal derived from different sources of information present across behavior and context (and device GPS), but only using it as a simple IP-based filter.