Remember when Panda used to mean a sudden increase/decrease for everyone on a single day once every 6 weeks or so? Back in March, Google said that they would stop announcing Panda updates because they were now part of the main algorithm as a rolling update.
New confirmation from Matt Cutts (at SMX in Seattle last week) means that they are currently being run once a month, but with the results of that update being pushed out over the course of the month.
