If we assume Microsoft's costs per employee are about $200,000 a year, the estimated payroll costs alone for Vista hover around $10 billion. That has to be close to the costs of some of the biggest engineering projects ever undertaken, such as the Manhattan Project that created the atomic bomb during World War II. And while Microsoft toiled on Vista, its stock price stayed flat.
So many things went wrong with the building of Vista that it's hard to know where it all started. The original code name was Longhorn, kicked off in 2001 after Windows XP shipped.