I got my iphone 3gs yesterday and today when i set up my gmail accounts, i was receiving duplicate emails - i am deleted the accounts and set them up again, but same thing happening. it doesnt happen with every email, just every other one or so. any idea why this is?
Go go Google and search "iPhone gmail IMAP". Google has step by step instructions that are very easy to manually set up Gmail for proper IMAP support. Just putting in your info into the iPhone's email client can cause random issues for certain people.