Valiant efforts to interpret these rules are being made by the International Private Equity Valuations Board, an industry body that some buy-out firms support.

Terra Firma, a British outfit, has struggled to keep control of one of its main portfolio companies, EMI, a record label, which it bought in a highly leveraged deal in 2007.

In its IPO prospectus, Blackstone said that although it's going public, "It is our intention to preserve the elements of our culture that have contributed to our success as a privately owned firm."