I imagine skyhook should have enormous leverage here. They business is normally the opposite, but it's foolish for them not to use their databases in the reverse. Same applies to large skyhok users such as Google and Apple, as they should have access to all of the same data.
Next, there is Amazon - they know where you live and they know your IP address. Everybody shops at Amazon.
Now, I can't think of an open & free way to collect exact information yet... ideas?
Good ideas but there are issues with this approach. But to explain them here would probably cause me to run out of characters and bore 99% of HN readers. But you're absolutely right that some of these sources could help augment the accuracy of any IP geotargeting system. Unfortunately this type of data has been hard to get a hold of because of either privacy policy issues or some strange beliefe that this was proprietary/trade secret information.
Trust me, I've tried this in the past and came up empty most of the time. That said, it is a really good idea.
Next, there is Amazon - they know where you live and they know your IP address. Everybody shops at Amazon.
Now, I can't think of an open & free way to collect exact information yet... ideas?