"Mr. Thomas is convinced current regulations will keep it capped."

John Paul Newport profiled Frank Thomas and his new book in the WSJ and it's interesting to read what he thinks has slowed down distance gains.

Mr. Thomas, who in 1984 revised and strengthened a regulation specifically banning spring-like effect, believes the USGA should have stopped the new clubs with spring-like effect as soon as they were discovered, because they only created potential expense and problems for the game (such as the need for longer courses) and violated tradition. "The first paragraph of the first equipment regulation published by the USGA in 1909 prohibited clubs that 'contain any mechanical contrivance, such as a spring,' " Mr. Thomas noted. But instead, over his objections, the organization in 1998 merely set a limit on spring-like effect a little above the then-current levels. That decision, he believes, was primarily motivated by fear of lawsuits from clubmakers who were already marketing the clubs.

Combined with simultaneous advances in ball technology, swing-motion analysis, player training and agronomy, spring-like effect boosted the average drive on the PGA Tour an alarming 24 yards from 1995 to 2003. But in the last five years the distance creep has slowed (the average is actually down a bit so far this year) and Mr. Thomas is convinced current regulations will keep it capped.