Users hate your cache
Users don’t like caching! They want to see the changes immediately. Otherwise they get confused and write you bug tickets or flame mails. But if you do not use caching the user comes and make your CPU’s burning. If your site is down you not only get mails from your users, but also from your management.
We worked hard on the right caching strategy over months now. But there are still caches that do not get invalidated right or are cached too long and we still get complaints from our users. So we decided to integrate a feature that allows certain users to invalidate the cache on the server side. The first idea was to add a link to every page that will append a GET-parameter to the site and then avoid the cache.