This is not exclusive to Google but since mine and most everyone's referrals are mostly Google I put it here.
In 2003 and especially in February I have noticed extreme variations in Google.com and Yahoo as well as Ink fed and other referrals to my Canadian site.
Some days - like Saturday - U.S. referrals will drop dramatically even though Canadian and world referrals stay more or less the same. I mean drops much greater than my usual daily variation pattern.
I am not talking U.S. only holidays like President's Day, I am referring mostly to Friday and Saturday traffic in 2003.
Anyone else noticed this or have any ideas?