The Department of Public Instruction web site includes data on AP courses offered going back to 1996-1997 through 2003-2004. (I apologize in advance for the long URL) The data is presented on statewide and individual district and school levels, which makes comparison possible:
http://data.dpi.state.wi.us/data/graphshell.asp?fullkey=02326903ZZZZ&DN=Madison+Metropolitan&SN=None+Chosen&TYPECODE=6&CTY=13&ORGLEVEL=DI&GRAPHFILE=GCOURSEOFFER
The page also has a utility that allows comparisons between districts and schools using pre-defined sets (ex. Big Eight) or user choice.
The user will need to use the links to view data for individual subject areas (math, foreign languages, English, etc.). The menu pick for statewide data is in the left hand column of the page. If I read it correctly, the number of AP course offerings is going up across the state, down in the Madison Metropolitan School District. At least in English AP offerings.
I note that haven’t had time to do a thorough analysis and have some questions about the data, and encourage others to do the same. I believe that there is some useful information through this source.