They're here--sort of. Twitter has launched the early beta phase of its "verified accounts" program, a background-check for celebrities and other prominent users of the service to weed out impersonators and fake accounts. If they pass the test, they get a graphic "badge" much like a PayPal verified account's.
"We're starting with well-known accounts that have had problems with impersonation or identity confusion," an explanation from Twitter read. "We may verify more accounts in the future, but because of the cost and time required, we're only testing this feature with a small set of folks for the time being. As the test progresses we may be able to expand this test to more accounts over the next several months."