I installed "Keep Drive Spinning" and set it to 4 minutes since Western Digital external green drives put themselves to sleep after 10 minutes of inactivity. Well, I just came upstairs from watching a movie via XBMC off a hacked AppleTV in another room that was accessing a movie from that 3TB USB3 external media drive and I came up maybe 3 minutes after the movie ended and watched as the drive went to sleep right before my eyes and then woke itself up a minute or two later again.
The point is that the Western Digital drives are set to 10 minutes internally, not 2-3 minutes. It's OSX that will often shut down a drive after only a couple of minutes of inactivity (certainly much faster than the firmware does anyway). This only started with the 10.8.5 update. I'm guessing that Apple somehow screwed up their own setting and even though I have it set in preferences to NOT put the drives to sleep, I think OSX is putting them to sleep whether or not it's checked since the update, perhaps even at irregular intervals. Something is definitely not right. Everything was working perfectly fine with 10.8.4.
The update also messed up some kind of setting in SMBUp (which puts Samba 3 on Mountain Lion since Apple's custom SMB setup does NOT work right with XBMC). However, re-installing SMBUp seems to have fixed that problem (so far it seems).
I have to give a big thumbs down to 10.8.5. I see no obvious improvements in day-to-day use, but they managed to damage drive sleep (and computer sleep as well for many by the sounds of it) and my networking setup. Way to go Apple!
Edit:
I tried a setting of 60 seconds for Keep Drive Spinning and the drive still went to sleep for 30 seconds or so just a minute ago and then spun back up. It seems the signal to make it sleep now is being sent REGARDLESS of disk activity (OR Keep Drive Spinning isn't working with 10.8.5). It's unbelievably annoying to have that drive spin down when you're using the computer.
