In his latest post, Jonathan Snook talks about the good and bad askects of a bit of functionality in the CakePHP framework - View Caching.
The view caching in CakePHP 1.1.8 is both good and bad. It's good in that it can dramatically speed up the performance of your site - when you can use it. And that's the downside. There are certain situations when it simply will not work as a practical option.
He talks about how it works and some of the limitations that it has (such as not being able to cache something not associated with the URL), and some people working on a solution. He also suggests two other solutions - (correct) url-based caching and cookie/session-based caching.