Lapizuli - 5:59 am on Sep 20, 2010 (gmt 0)
I haven't seen these kinds of delays on my tiny sites or pages, that I can recall.
Could this be an artifact of reporting delays with the stats programs? As in, it's the reporting that's bottlenecking, not the SERPs?
If it does exist, my first instinct is to think it's nothing nefarious, just Google doing some form of systematic testing, or down servers, or a bug.
In the event that it's server-related, it could be useful to know the locations of the websites this happens to, and of their primary markets, and how geographically narrow they are.