Ubuntu 12.04 (Precise Pangolin) is getting closer to launch, but some of the bugs have not been iron out yet. It seems that the Hibernate function is one of them.
The Hibernate function won't be available in Ubuntu 12.04 (Precise Pangolin), at least according to some discussions that took place on Launchpad these days, where a bug was submitted.
It appears that hibernation is disabled by default in Ubuntu 12.04 and there is no option available to enable it, unless you are willing to doodle with some configuration files.
The bug or at least the lack of this feature will affect all of the Ubuntu derivatives, Kubuntu 12.04, Lubuntu 12.04, and Xubuntu 12.04.
According to some of the comments made regarding the bug, it appears that this function affects a number of users in the previous versions of the Ubuntu operating system and made them lose important files.
We'll keep you informed if Canonical decides to implement hibernate again!