I have the same issue. 2009 MP Quad 266.
A short sleep-10-30 minutes it will wake fine. Longer than that and the power light is no longer pulsing, the screen stays black, no activity. Have to do a hard shut down.
I am going back to 10.8.1
seems like Apple is getting more like MS every OS rev. I mean heck look at the icons ion this message bar! Looks like Chrome. UGH
Same issue with my Mid 2009 17" MBP. I just disabled wake on LAN, so we'll see what happens in the morning. Also had issue with Time machine stalling out. Was on phone with Apple support for 1 1/2 hours without success. They claimed to be unaware of my latter problem as I read them a post from page 6 of 16 of this forum.
I ended up fixing it myself by deleting the last partial backup I found on my Time Machine disc.
Any more problems and I'm going back to 10.7 - I agree with many that Apple is getting much like Windows with each OS 'upgrade'. Maybe I'll try giving 10.8.2 my cat's worm medicine....
Two calls into tech support, but I think they may have helped me fix this.
remove any third party software and set aside. (they told me I could keep some adobe, microsoft and HP items)
System Preferences --> Users + Groups -->Login Items
remove any third party stuff from in there.
I'll know tomorrow morning if this REALLY works, but it dfefinitely allowed my computer to sleep and wakeup over a short period of time.
Alright - regarding my previous post of cleaning out launch agents - none of it actually mattered.
After cleaning the launch agents and startup the computer allowed itself to go to sleep from the apple menu, but not on it's own. THAT was actually the problem - it would never GO to sleep - and once displays were down - game over.
Final answer, after about 6 calls to applecare:
boot to recovery disk by holding down option key
reinstall 10.8 (which actually installs 10.8.2)
stuff seems to be working as it should now.