John Lim has this new post on PHPEverywhere today concerning some of the finer details of Internet Explorer's Caching Behavior.

There's a new MSDN article on HTTP Performance that describes IE's caching behaviour: The vast majority of users leave the setting at the default of Automatically.

The most important fact to keep in mind is that these four options mostly impact the behavior when there are no caching headers on the HTTP responses; when caching headers are present, Internet Explorer will always respect them. The following table describes the impact of these settings on request behavior.

There are a few requirements that a page must have to meet in order to request the page again: "content-type begins with image/", "resource has a last-modified time", "the URL to the request doesn't contain a question mark", and "the cached resource has been conditionally requested at least once within the most recent 25 percent of its overall age in the cache".

John also mentions another resource to check out - Caching Tutorial for Web Authors and Webmasters.