I won't pretend to understand the hardware mechanisms involved, but it
does work. Think it's something along the lines of hibernation not being
fully off, but a small current being maintained to vital areas, but you
will probably find a better explanation via google.
The best thing to do is to try it. Schedule notepad to run in say 5
minutes time, and put your computer into hibernation mode. The only
proviso is to check the 'Wake the computer to run this task' checkbox on
the 'Conditions' tab for the task.
It's also a very handy technique for running tasks that you'd perhaps
rather not be around for eg defragging of drives, periodic chkdsks, etc