I have a Fedora 17 desktop system running the latest 64-bit kernel which will not go to sleep properly. I know this because the fan continues to run after the screen has blanked - further the system will not restart when I repeatedly whack the keyboard with my fists. Smashing it against the sideboard also has no effect.
If I shut the machine down it will wake successfully on a light keypress.
I would appreciate any suggestions as to how to come to a diagnosis for this as there seem to be many users experiencing this issue but for a wide range of reasons.