Back in March, Google said they will stop confirming Panda updates because they are now more baked into the index and algorithm.
Well, at SMX Advanced, Matt Cutts of Google announced it is still roughly updated monthly (although it has been 6 weeks because they are trying to soften Panda - note, next Panda update sites should be released) but these updates are rolled out gradually over a 10 day period. (How is that for a run on sentence?)
So, Panda might be pushed out on the 1st of the month but take ten full days to fully roll out everywhere. Then it will happen again roughly a month later. So 1/3rd of the month, Panda is rolling out. I called this at Search Engine Land, the Panda Dance.
For more details on the Panda updates, click here.
Forum discussion at WebmasterWorld.