Microsoft co-founder Paul Allen just upgraded his digs on the Upper East Side, buying the $25 million penthouse in the building he already lives in at 4 East 66th Street. Allen bought into the chichi Manhattan co-op in 1996, paying $13.5 million for a "behemoth" unit on the 11th floor, and now he's got the seven-room top-floor unit as well for extra duplex fun. [New York Observer]
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