Matt Cutt confirmed what WebmasterWorld users have seen on a 40+ pages thread at the beginning of october, an algorithms and scoring change. For the first time, one client lost his first page on his main keyphrase and been pushed on page 10. Ouch !
It's a good thing his site is bilingual and with the french keyphrase he is still on page 1. I personnaly think he will retreive soon his good spot, because it's not normal for a site who was not update in the last year to been pushed so far away. Also when your keyphrase bring a few directories site your in, before your own site, that's definitively a bug.