It is actually not that strange at all. A cache is designed to take images, backgrounds and other "static" information from web sites and copy them onto your local hard drive. The next time you visit that site your browser looks to the hard drive first and then downloads anything different. This dramatically speeds up web browsing since it doesn't need to download everything over and over again. It is a little less dramatic today with broadband, but in the days of 56k modems the speed improvement could be very significant.

Problems can happen when your browser gets "confused" (technical term) about what is static (such as the repgeek logo at the top left) and what is new information (discussion threads). Clearing the cache (and browsing history for good measure) forces your browser to treat everything as new again.

OK, not precisely what happens technically, but you get the idea.