Every few days, certain websites will appear to be down. Restarting the DNS service or clearing the cache resolves the problem for a few days. Then the problem occurs again. It is always the same websites. The one we use most often here (we are an audio electronics company) is GearSlutz.com - we advertise our products on this site and we also (as musicians and recording engineers with day jobs) use the site for both personal and professional reasons. This site is always one of the sites that stops working till the cache is cleared.