I can’t quite pin-point the date, but Google have changed the way they fight spam. It’s a dramatic shift that can only have come from a change in policy internally. This schism from their own way of thinking is dramatic and perhaps an end of innocence from the Webspam team.
For me the first indication of this shift was when Google started naming their updates again. Vince and Panda (and Caffeine, even though it wasn’t technically a algo change) this was a change from the ever-flux where changes were being made constantly in small iterations, why did they make this change? Perhaps it was just because they were big cohesive changes, or partly it was because Google want to talk more publicly about what they considered good and bad content and they wanted to show that they were taking action.