I have not done any experimenting myself but have heard of people using Geotargeting on Google's content network, and this being very profitable has anyone had any experience of this? below is an example of what i mean for people who might not have heard of it. http://www.seoresearchlabs.com/images/adsensegeo.jpg
I manage a lot of geo-targeted campaigns for local business, and dependant on your product/service it can work out great. For example if your business only ships to a selected area, geo-targeting is a no brainer. If though, you know that a certain area of the country are more likely to buy your product, then geo-targeting them can increase your ROI. Something to be aware of however is that geo-targeting is not perfect - a customers location is based on their IP address, which depending on how far away they are from their ISP's local exchange could be quite away from their actual location. Not so much an issue for the USA, perhaps - but here in the UK users sometimes appear to be halfway across the country from where they are actually sitting!