If you've ever had the frustration of working with Ajax in Internet Explorer and have noticed it caching the requests/results, you might want to check out this new post on the JSLabs blog for a helpful hint.
While working on an AJAX project over the weekend, I ran into the following issue: (through a GET request), every time I tried to call a certain function, It was returning the same data (which was supposed to be different each time)
First, he tried just changing the headers (via PHP's header function) to see if IE would understand the new message, but to no avail. He finally figured out that, despite whatever headers were sent or how much the content changed, what he really needed to do was to provide the script some kind of unique identifier with each request (just appended to the url) so that IE knew the request was different. His weapon of choice was a date/time value.