Receptional_Andy - 10:21 pm on Jul 7, 2010 (gmt 0)
it would not lead to duplicate content penalties and ranking problems
Google has a process to prevent the possibility of showing the same content from a number of different URLs. This process is complex, and there is potentially serious detrimental impact from getting caught up in that process by reproducing content in an uncontrolled way. In terms of real world experience, I have yet to see a positive side of producing identical copies of the same content at different URLs. Even spammers don't do it ;)
If you produce genuinely regionalised versions of your content, then you have the potential for a great expansion of your coverage in search results.
My experience of the GWT option - your mileage may vary ;)