[eluser]Steve Grant[/eluser]
As far as I'm aware, nothing's changed regarding sessions between 1.6.2 and 1.6.3.
The CI class doesn't utilise the native PHP session class, which means that (unless you use a third-party session library/plugin) if a user doesn't allow cookies in their browser, you won't be able to retrieve or set any session data. Which is annoying.