We all like our website to be as fast as possible (that's one of the reasons why we love .NET, right! :-)
A couple of minutes spend optimizing your IIS settings can also have a huge impact on the load time of your pages. Your website probably uses quite a few (semi) static files, like images, css and javascript - As these files does not change very often, there is really no need for your users to download these files every time they visit your site.
To cache these files, simply tell IIS to add cache headers. It's really simple to do:
1) Open IIS and locate your site.
2) Right click e.g. the "images" folder.
3) Select properties and choose the "HTTP Headers" tab. Check the "Enable content expiration" and set "Expire after 5 days".
The browser now compares the current date to the expiration date to determine whether to display a cached file, or to request an updated file from the server.