Couple of things, ya'll:

JoeZ,  in reference to your question about surround back speakers. You can expect a more dramatic effect from surround back speakers if they are placed well behind you and more or less aimed at your listening position. As convenient as the in-ceiling speakers are (I use 'em!) the one thing you just can't get around is that they are shooting the bulk of their sound down toward the ground. There's this cone of covereage that you need to be located under in order to really get the most out of them. This is why I enthusiastically recommend them as surround speakers, but rarely as rear surround. The distance needed between the listener and surround back speakers to really add depth to the presentation really puts an in-ceiling speaker too far back to be as effective as most of us would like it to be.

 JonL, as for height speakers, it may interest peeps to know that the use of in-ceilings isn't actually being suggested by Dolby and DTS. At least, not in this quote from DTS' R&D VP, Paul Smith:

In an 11.1-channel DTS setup, the left and right height speakers would be placed above the left and right main speakers. The distance between a height speaker and main speaker would be the same as the distance between the main speaker and center-channel speaker, said Smith. The six surround speakers would be arrayed like this: On the right, one speaker would be placed at 90 degrees from the listener, with another at 120 degrees and the third at 150 degrees. The left-side surrounds would be likewise positioned.