Warning, this is a techie post.
I recently had an issue with Internet Explorer recently when using getJSON to get a result set from the server, however the client browser was displaying an old version of the result set. After a little digging, I found that IE caches ajax transactions by default. Personally, I think this is daft, as I generally want to request new data from the server the majority of the time. From this point of view, I think it would be better to have caching disabled by default – but there you go!
To get around this problem, simlply disable ajax caching after page load (i.e. $(document).ready()).