If you’re experimenting with Cache-Control headers (set in IIS via the file/folder properties dialog, HTTP Headers tab, “Enable Content Expiration” checkbox) there’s a great summary here:
http://www.mnot.net/cache_docs/#CACHE-CONTROL
Also, remember that F5 forces the browser to re-check all files, even those that would normally be cached. Not that I made that mistake or anything… 
It does make sense to tag certain rarely-changing files (eg, images, css, javascript, etc) on your website with an expiration date, even if it’s only for one day.