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The first naysayers to come out swinging against the crazy valuations of sites like YouTube ($1.5 billion), Facebook ($2 billion), and MySpace (a ricockulous $15 billion) are reporters and bloggers, and a few analysts known for a healthy cynicism. Slate writer Daniel Gross, for example, today praised the role of skeptics in the social-network-valuation boom. But who'd expect Mark Cuban to join them?

Cuban, the billionaire owner of the Mavericks, investor in blogging company Weblogs Inc., and host of a failed reality show aping Trump's "The Apprentice," made his billions in 1999 by selling online video startup to Yahoo for $5.7B in stock. Now a man who owes his fortune to a puffed-up valuation is calling out YouTube, saying, "anyone who buys that is a moron."

Cuban delivered a whole little rant to attendees at New York's Advertising Week. Reuters quotes him: "There is a reason they haven't yet gone public, they haven't sold. It's because they are going to be toasted."

Slight caveat: Cuban needs to brush up on his numbers. He asked, "Somebody puts up something really good and you get, what, 60,000 viewers?" Actually, it's not hard to break a million. But since Mark's an expert in worthless but overhyped companies with ludicrous sale prices, we'll take his word about YouTube being toast.

Only a "moron" would buy YouTube, says Cuban [Reuters]