I recently came across an issue with IE
caching responses from ajax requests.  My ajax code would send an
HTTP GET request if the querystring was less than 2067 characters and a
HTTP POST if the query data was larger.  When IE caching was set
to Check for newer versions of stored pages:
automatically, IE would cache the GET web response.  Changing the
ajax code so that it always performed HTTP POST requests fixed the
weird issues I was seeing (related to requests being cached). 

IE properly caches GET requests but doesn’t cache POST requests. 
So, I could have either altered the url of the GET request to be unique
everytime or I could have set the “Expires” header to -1.  I chose
to just use POST requests since I don’t want them to be cached
anyway.  More information can be found on the wikipedia page.

Anyway, hopefully this will help someone that runs into the same situation.