Is there data on the geographic distribution of bitcoin users? If you are a company wanting to adopt bitcoin as a payment method or an academic wanting to study the bitcoin market it is important to know as much as possible about the bitcoin users. Since bitcoin is pseudonomous it is hard to gather direct information on the users. However, if users want to make transactions then they need to broadcast to the network. Although the IPs are not stored in the block-chain, there are ways to learn them. With the IP addresses, it is possible to use IP Geolocation to get an idea of where the user is. Hence the question:

Is there data available on the geographic location of users of bitcoin? Especially on volume of bitcoin transactions from given geographic areas?

Or is it impossible or unlikely that such data can be gathered? If the majority of users use Tor for instance, then it would not be possible to get a good location data. Are there other technical constraints that make it impossible to use this or other approaches to learn the geographic locations of a large number of users?

Meta note
Since bitcoin is new, it is possible that such data is unavailable yet just due to the novelty. Please don't provide such answers, we can just wait until such a study is done and given as an answer. A 'no' answer is interesting only if it explains a technical constraint that would stop such studies from ever happening.
Also, it is possible for a committed user to invest effort in order to hide their location. However, unless there is reason to believe that most users use such efforts, this is also not a very relevant answer.
This question is an attempt to turn our lowest voted question into a legitimate specific question.
This shows bitcoin nodes based on IP address location.

http://www.weusecoins.com/globe-bitcoin/  (UPDATE: link is broken)