What's last situation with the CI Session Class?

[eluser]WanWizard[/eluser]
The session class never had any bugs with IE. Your configuration could though (IE doesn't like an underscore in the cookie name for example).
It is also very important to configure all settings properly, and according to the RFC specs. Browsers are getting more and more strict when it comes to cookie configuration.

It is a lot more secure than PHP own session management (which is not secure at all), so switching to something that uses that is a very bad idea. Don't forget to use database sessions (no user data stored client side), and to encrypt the session cookie with a random salt.