I just added a document to the IE7 usage section outlining some ways to improve performance of your IE7 installation.
Although these guidelines apply only to IE7, it is woth noting that the first one can be applied to all web sites. Internet Explorer has some well known bugs. It also has some drawbacks which are not well documented. One of these is its poor caching. An obvious side-effect is the image flicker problem but this can also affect other aspects of your page (DHTML Behaviors particularly suffer). I strongly recommend httpExplorer as a way of inspecting HTTP requests sent by Internet Explorer.
It is worth noting that all files served from the W3C’s server have expiry headers.