Apparently, Facebook tracks this stuff and reports that last Tuesday, 2.7 Million people more than usual, changed their profile pic. That seems like a lot to me.
Here is a image that shows where the profile changes were geographically by county:
(Click on image to enlarge it....)
The darker areas represent a higher number of those people who changed. Lighter areas showed locations where there were fewer profile pictures changed.
Facebook also has information available on when the changes were noticed by the researchers at facebook, as well as the demographics involved. Generally speaking, most of those who changed their pic were 30-somethings, with a very slight higher percent of women rather than males making the change.