I know this isn't exactly what your after but it might help a bit. I've put the ip address that relay the most blocks on a globe here.http://blockchain.info/nodes-globe?series=topBlockRelay
This mostly shows the locations of the major pools. BTC Guild & Deepbit are both hosted by the same company in germany so that is why there is a spike such a huge spike.
Since people mining on pools may also have a client running to get their payout, the current node distribution can give a rough estimate of the interest,
adding to this, temperature, cost of electricity and GPD.
These country are at the top of hashing power :
... ukraine, finland ...
(ignoring electricity above 12c/kwh)
Might be interesting nonetheless to have more accurate measurements that only pools can provide.