A bet on the future of office rents is behind Blackstone Group's $33 billion bid this November for Equity Office Properties Trust. Since its founding in 1976, the real estate investment trust chaired by value king Sam Zell has snapped up properties to become the top owner of office space in the U.S. Private equity firm Blackstone proposes to take Equity Office private in what would be the biggest leveraged buyout of the year. Although Equity Office comes with staggering debt, Blackstone has made successful bets before: it began buying up hotel REITs in 2004, just before room rates shot up. Zell's reported take from the deal: $660 million.