RichG, they tell the system to ignore the cookie it's placed on your system and to treat your visit as the first time. That may have an adverse effect on the colors of folders and other visual indicators that let you know you've already visited an area, though.

How a refresh button works on a browser is dependant upon the actual browser, but the normal behavior with refresh buttons and framesets is to load the overall frameset again (which then pulls in the original page for it). But, again, this varies depending on your browser and operating system.