Over the last couple of months I've been closely monitoring Google results on a number of data centers for signs of the Google Caffiene update. For the last month the data center that my browser was pointed to has been serving two different indexes every half hour or so.
Yesterday, for the first time, I saw the newer results stick around all day long. Today, they seem to be jumping again. Good news for my clients is that the new results are consistently showing better ranking results for their websites.
Here is a thread following Google Caffeine: DigitalPoint.