g1smd - 11:53 am on Jul 23, 2008 (gmt 0)

Way back, like in 2003 or something, it was often signal that an update was about to occur.

In more recent times, I guess the processing power is being used for some other purpose, spidering given a lower priority for a short while.

I've written stuff about this a year or so back, but I don't remember the details now. I've learned not to stress about day-to-day fluctuations too much. If I see something that appears to be going wrong, I check for obvious technical problems with the site, then wait a week or so and see if Google reverts - they always do.