I did place the front ones high, the center one I left on top of the TV. The receiver had a setting to specify if the speaks are placed high or low, so I don't think its that big of a deal, and I've tested it out for 3 days with them up there. Sounds great. Soul is right, I cant go through the ceiling, etc.
The mounts I bought for the sony speakers only go about 45 degre angle, so what I think I'm going to do take a small piece of wood, cut it on a 45 angle, so the rear speakers will be able to point directly towards sitting area.
BTW, from what I read, the rear speakers are typically the same distance away as the front ones? Correct? ie. My front speakers are 10 feet away, so I put the rear ones 10 feet away as well. (although I know the receiver does have settings for the distance of the speakers).