"Is Hybrid Sleep on Windows 7 the same as on Windows Vista?
In a word, yes.
In Hybrid Sleep mode, the system saves any open documents and programs to memory and to your hard disk, and then puts your computer into a low-power state as in normal Sleep/Standby state.
An advantage of hybrid sleep is that if a power failure occurs, Windows can restore your work from your hard disk. If a power failure such as a power outage occurs when your work is saved only to memory (as in Sleep mode), all work is lost.
In Hyrid Sleep mode, if the computer suddenly loses power, users can still recover to the last working state as when the computer enters hybrid sleep mode, because all data in memory is saved in the hiberfil.sys hibernation file. In this case, the computer is acting exactly the same with hibernation mode to resume computer activity and yet still enjoy the benefit of fast return to full operation from Sleep mode.
I've read somewhere that hiberfil.sys file is usually 75% of your RAM size. It's a reserved space, so it's actually locked all the time. Of course Windows would normally write to disk only the contents of RAM (which you can easily check by openening Task Manager with CtrlAltDel and going to Performance tab), so you might want to check a few (dozens) times how much memory is used during your normal work (or at the state you might put your computer to sleep) and reduce the hiberfil.sys size.