Codeigniter's built-in page cacher

[eluser]pickupman[/eluser]
This issue has been discussed many times here in the forums. This is why you have some people develop other cache libraries in CI. As been discussed before, extend the core to check for user sessions before fetching a cached page. Or, as others have done, is grab one of those other libraries, and only cache the content that you need cached. The problem with CI's implementation is that it is all or nothing. I personally have used Phil Sturgeon's cache library and like it a lot. You can cache calls to functions in libraries, models, or any other data. Simple syntax and really solves the issue you are discussing. MP Cache is another popular partial caching library.
You could even use Phil's library to cache the output from a view, and retrieve for a not logged in user.