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Three of today's stories provide a perfect lesson in recognizing a bubble. The astute reader will recognize the common themes.

  • Social site rejects mad money: Facebook's not the only social site hubristically turning down generous offers. International site Bebo just said no to a $550 million buyout, according to the blog TechCrunch. The company's holding out for a billion-dollar offer, which it just might get — unless the market tanks this year. Then Bebo will have to wait for a lowball offer, just like Tribe Networks. [TechCrunch]
  • More free VoIP services: Skype, which is already providing free domestic computer-to-phone calls on its network, now offers free international calls. The company says it will profit from add-ons like headset purchases — until it starts giving those away. No wonder eBay's market cap has dropped ever since it bought Skype. [Skype]
  • Lively dot-com gets a lifeless competitor: See, old-school pet site Dogster is cute, friendly, and human. Newcomer pawspot is cold and forgettable. Guess which one will get more VC funding. [TechCrunch]