This is good news. It should have a large impact on our understanding of how PD is distributed, and this may give us clues as to the aetiology of Parkinson's.
For our present understanding, see the paper by Willis et al., 2010:
"Geographic and Ethnic Variation in Parkinson Disease: A Population-Based Study of US Medicare Beneficiaries"
Geographic and Ethnic Variation in Parkinson Disease: A Population-Based Study of US Medicare Beneficiaries
The maps, at county level, are especially interesting.
John