Nate Silver at FiveThirtyEight has done some interesting statistical analysis indicating that the April 15th tax day "Tea Parties" may have been more about (small "L") libertarian backlash than a broader Republican based movement.
Nate draws the connection between per capita contributions to libertarian Republican Presidential candidate Ron Paul and attendance at Tea Party events. Campaign contributions are a strong indicator of not only support, but of enthusiasm.
To account for uneven attendance reporting, Nate measured per capita attendance by region dividing the US into 11 regions.
The result seems fairly clear:
