Codeigniter's built-in page cacher

[eluser]pickupman[/eluser]

Can’t you just put the cache command inside an IF statement, that checks to see if the user is not logged in?

No, CI will first look in the cache folder for the page before doing any processing. If a page is found in the cache it will be output to the browser, and your controller is never loaded. That's why it caches the whole page rendered, so it doesn't have to re-render/process the pages again.