The financial regulation bill that Congress just passed, after fierce lobbying by banks, is aimed at curtailing some of the practices that caused the financial crisis. But much of Wall Street has mostly gone back to business as usual. Nowhere are the potential conflicts more apparent than on the trading floors, where executives must balance their pursuit of profits and their duty to customers.

In addition to losing money for New Orleans workers and others, securities lending also played a central role in the near-collapse of the American International Group. Through securities lending, pensions and mutual funds borrow money to make trades, adding to the risks within the financial system.

Lawsuits are flying against JPMorgan and others, including Northern Trust. Clients say that they were not warned of the risks associated with this practice and that the banks breached their fiduciary duty. Wells Fargo lost such a suit over the summer and was ordered to pay four institutions a combined $30 million. The State Street Corporation, which took a $414 million charge in July to cover some of its customers’ losses, faces suits from other clients.

Representatives for these banks said the companies had acted appropriately and that they intended to fight the suits.

Despite such troubles, the securities lending business has rebounded after plummeting during the crisis. Today shares with a combined value of $2.3 trillion are out on loan, according to SunGard, which provides technology services to financial companies. In 2007, before the bubble burst, the total on loan was worth $2.5 trillion.

The quick revival of securities lending raises concerns about whether banks and their pension customers have learned any lessons.

“What happened was the banks got greedy and they looked at the return they were getting on the collateral and said, ‘Why don’t we go further with this?’ ” said Steve Niss, the managing partner at the NFS Consulting Group, an executive search firm specializing in investment management. “But the clients got greedy right along with the banks.”