The Roman Senate had nothing on Yahoo. The Web 1.0 giant's biggest investors have no qualms about pulling out the knives and carving up CEOs. Like Carl Icahn did in June 2008, when he tried to oust Chief Yahoo Jerry Yang to force an acquisition by Microsoft. Or, more recently, when Yahoo investor Dan Loeb gutted new CEO Scott Thompson just five months after he assumed the big chair in January 2012. Thompson's mistake: He fibbed on his résumé, claiming a computer science degree he did not possess. Our advice to Marissa: Sleep with one eye open and a knife under your pillow.