TheMadScientist - 9:13 pm on Nov 30, 2012 (gmt 0)
It seems to have taken a few days for the effect to be noticed, at least for us. Possibly a result of the Thanksgiving/Black Friday weekend? The big boost in traffic came on Monday.
I noticed this in the reports here myself, and another theory I have for the lag is:
We know they only run Panda on occasion, because it's 'too big' to be an 'every day thing', so maybe the report of the date is when it was started rather than completed and the noticed effects of the run take time to 'push' completely into the live results, and, in my opinion, changes could quite possibly be (likely are for something that big) pushed in 'segments' so some those in a 'result segment' where the run is completed first might notice a change sooner than those in a later 'result segment'.
* I haven't bothered to look for a definitive answer, because I figure I'll see the changes when I see 'em and why there's a lag between the announced date and seeing changes isn't something I think of as critical. It really doesn't make much difference to me, so it's more curiosity than anything.