Hibernate isn't sleep, its just incase well its more a laptop issue, if your computer runs out of power when the lid is closed or its a sleep.
If you plug it in and give some power it will wake up from where you left off.
Sleep is separate from my understanding.
That's what I thought, but learned differently. Well, read my thread, a few people taught me a few things on OS X, I was very grateful.
OCZ Vertex 2 in 2010 Mac Pro 6-Core - Known issue with Sandforce SSD's
You can check if you are using hibernation mode using pmset -g in terminal.
See this Macworld article about it:
http://www.macworld.com/article/53471/2006/10/sleepmode.html
-Kevin