I have just updated my Xubuntu 13.10 to 14.04. Did not change anything. Suspend-to-RAM (standby) and hibernate both worked well in 13.10.
Now hibernate does not work any more (suspend-to-RAM still works). The machine seems to suspend to disk, but after a restart, I just get a blank screen and the hard drive is running.
What can I do?
After two months of investigation (no one could solve the problem so far), I found that under the newest Debian (XFCE) with kernel 3.2.0 hibernation works correctly. The same holds for Linux Mint Debian Edition (LMDE-201403), which is based on Debian.
Hibernation does not work under the newest Linux Mint 17 "Qiana", which is based on Ubuntu, nor under the newest Fedora 20, nor under Xubuntu 14.04. They all have a kernel version around 3.13.0.
So my conclusion is that there is something wrong or misconfigured with the newest kernels, and since the distributions that are not directly based on Debian use the newest kernels, their hibernation does not work correctly, whereas the Debian kernels do work.