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"My Flickr account is my Yahoo! account. If I use Yahoo! Mail, it’s my e-mail account. If it’s my e-mail account, it’s Single Sign On for basically everything I use online thanks to forgotten password e-mails. It may not be an internet banking account but it’s only one step down."

Simon Willison nicely sums up why OAuth matters, in a discussion about suspicious behavior by the iPhone app “Exposure”