RalphJohnson said this on the XpMailingList (http://groups.yahoo.com/group/extremeprogramming/message/33020):
In chapter 3 of RiseAndResurrectionOfTheAmericanProgrammer, page 63, EdwardYourdon gives some statistics from studies about OOP projects. It seems that early OO projects were measurably more successful, but later ones did not score higher than the average score. Yourdon's speculation for this change is that early projects had more "fanatics" on them, but later ones had a more mixed crowd who got into OO for money instead of a personal like. This implies that a programmer's personal preference is more important to getting results than the language or paradigm itself.
See also ProgrammingIsFun