Since upgrading to 10.8.2 I have had this issue.
I have 'Wake for Network Access' enabled but I am unable to wake my Mac Pro from my AppleTV2 using Home Sharing.
If I reset the PRAM, WOL works the first time the Mac goes to sleep but after that it wont work.
The Mac Pro still periodically wakes up (as in the fans and HDDs spin up, no GUI) to keep the network address alive but nothing can actually wake it, (except once on the first sleep after PRAM reset).
This was not an issue prior to 10.8.2.
I have also noticed since upgrading to 10.8.2 that after waking the Mac, it takes approximately 10-15 seconds for the network to re-connect. This is via a wired ethernet connection.
This also was not an issue prior to 10.8.2.
I really hope this is fixed with 10.8.3.
10.8.3 does NOT appear to fix this problem. I was hoping that upgrading my iMac to 10.8.3 would fix it. Well, as soon as it came out this week, I did the "upgrade". Result: no change whatsoever. Once the iMac sleeps, it cannot be woken via sleep proxy. My only option is to set it to "never" sleep. A lot of good all this elaborate energy saving infrastructure has done me! When is Apple going to get its act together? The most annoying part is that it used to work fine in Lion.
I had a similar problem trying to connect using parallels mobile and appleTV v3 over my home network. I read a post to change the service order, so I set Ethernet to the top priority and it fixed the problem last week. A few days later, I installed a OSX/itunes update and it stopped working again. Very frustrating. This issue is all over the forums. Not having reliable waking renders AppleTV useless. This used to work perfectly and the only thing that changes in my network is apple updates. Please fix Apple and verify before releasing new updates.
I've finally resolved this issue by doing a fresh install of Mountain Lion, overwritting the upgraded Lion system I was having trouble with. After clean install, I restored all users from Timemachine backups, but DID NOT restore System Settings (not sure if this matters, but I think it makes sense to avoid in this case.) It has been running for a few days now, and the machine's services remain available even when it sleeps. Wake on Demand seems to be working as expected now, including access from AppleTV.