I tried this out ages ago and it didnt really work. It was like half the system shut down but the drives and cpu fan kept ticking. I realised I hadn't tried it on my current hardware setup as I changed my motherboard for an Abit AV8-3rd Eye during the past two years. I just tested out hibernate and suspend and both worked fine. I ran into a problem with suspending the system where the monitor didnt resume but I found an easy fix for that. I wrote up what happens with each as I figured theres probably tons of other people who havent given it a go.
First I tried hibernate, this worked straight away. The first thing that it does is show the "Windows is hibernating" message box similar to when you normally shutdown albeit a different message. Then it switches to a lower quality screen whilst its preparing the save file and shows you a progress bar. Then the hardware shuts down.
When you press the power switch it does the normal hardware checks i.e. ide drives, raid detection etc. When it reaches the part where it normally shows the Windows loading screen it instead shows the new Resuming screen. Then poof...windows loads to the last state you were in, so if you had an unsaved word document open that would be displayed as it last was. Its pretty cool and took about a 3rd off my boot time.
Suspend was another kettle of fish. I use a Microsoft Natural Multimedia keyboard which has a "sleep" key on the top right. This is a shortcut to send the system into suspend mode. I cant change it to hibernate via the usual "configure your keys" app so instead of avoiding it I decided to try suspend out. Suspend does a similar shutdown to hibernate although the message is more along the lines of "Suspending Windows". It doesnt have the lower quality screen though and just shuts down after the initial message more like a standard "Shut down".
When I pressed the power button the system sounded like it was booting up but the monitor didnt come on. All the drives and fans kicked in. I checked my windows settings and found that there was pretty much sweet FA I could configure in Windows. I remembered that my bios had a couple of options but not what they where so that was my next stop. On the Power Management bios screen I had it set to "S3 Suspend to Ram" but I also had the sub-option of "Enable S3Bios on resume" ticked. I deselected that and then quit whilst saving the bios.
When Windows loaded normally I launched my text editor and tapped in a few lines. Didnt save the document and then tapped suspend and let it do its thing. Now here comes the truly, truly cool part, powering it back on. This happened almost instantly. No bios screen whatsoever. It goes straight back to my desktop in under 5 seconds.
I'm 100% sold on Standby mode, so what if any unsaved data will be lost if the power gets cut whilst its suspended, big whoop. I figure I'll still treat it as a normal "Shut down" by saving anything thats open, I think I'm too finicky not to do that anyhow. It just means my boot up times will be alot quicker.