Taken directly from amazon.com:

Do you live in one of the Harry-est Towns in America? Each week Amazon.com will update the Top 100 list of which towns in America, on a per capita basis, are pre-ordering the most copies of Harry Potter and the Deathly Hallows. Amazon.com will donate a $5,000 Amazon.com gift certificate to a charitable organization of its choice that serves the winning town. The winning town will be announced shortly after the deadline of 11:59 p.m. PDT on July 15, 2007.