Simsi - 10:45 pm on May 3, 2010 (gmt 0)
One of the interesting factors people are reporting - if I understand correctly - is that we are not just seeing a one time drop in ranking. Instead, it's a process of dropping a bit, then a bit more, then a bit more - and sometimes the pattern breaks a bit with a return to good rankings for a period.
I would have thought this was condusive to the theory that Google's new infrastructure allows them to better measure user behaviour. Knock sites up and down, measure user behaviour in different positions for different searches and gradually a more settled pattern will emerge. This can be achieved gradually with small jumps up and down - like continual A/B testing although it could take weeks, that's anyone's guess.
It also ties in with an infrastructure change which is likely required to collect and store the data, automate movement and measure the effects of each comparison.
Plus it strikes me as common sense to use the effectiveness of a site increasingly in rankings while reducing the effect of aspects that can be manipulated.
My positions yoyo daily at the moment and if I was a betting man, that's where my money would be.