My combination of a Microsoft USB Natural Ergonomic Keyboard 4000 and a Microsoft USB Dual Receiver Wireless Mouse was causing my PC to immediately wake after hibernating.  This was also causing S4 sleep mode in Vista to fail to wake up.

Normally the wireless mouse has a wireless keyboard as part of the package, but I'm only using the mouse so I think this was causing problems - my device manager showed two keyboards even though I only have one wired keyboard.

To fix this I ended up disabling both the keyboard and mouse (receiver) from being able to resume the PC.  You can do this using the command line tool powercfg.  Here's what I did:

powercfg -devicedisablewake "Microsoft USB Natural Ergonomic Keyboard 4000 (IntelliType Pro) (001)"

powercfg -devicedisablewake "Microsoft USB Dual Receiver Wireless Keyboard (IntelliType Pro) (001)"

You can verify the device are disabled using: powercfg -devicequery wake_armed

After disabling both of those, S4 and hibernation started working again.