Caching can actually make things worse sometimes. Like, when does it cause more problems than it solves?

We're thinking about putting in a cache for some reports that get used a lot and are pretty complicated. The goal is to make the UI load faster. But I'm worried about the cache getting old, since the data it's based on changes all the time. So, when does a cache actually make things slower, or cause more headaches than it fixes? I'm thinking about stuff like cache misses, how much harder it makes things for developers, and issues with the data not being consistent. Have you ever seen a situation where adding a cache just wasnt worth the trouble?