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Mark is spot on - If you have the time, creative and/or resources to write thousands of pages of unique that's your best bet. If you don't however, have you tried making sure that your title, h1s, metas, etc., are all unique? If not, I would try that and re-submit your site through your webmaster tools...that's worked with many of my clients and allowed the each child subdomain to rank regionally. It's not the ideal solution, but it's a step in the right direction that won't hurt.