Since my family room has seating up against the back wall, the up-firing design probably would work well for me. In a 5.1 setup, I'd put them on the back wall about 2' from the corners of the room.

I don't really have a good spot to put side surround speakers due to lack of wall space (fireplace and brick finish wall on one side, windows on the other side). Also the centerline of the room has to be at the 1/3 position into the room due to the location of the entry door near the only wall the tv can be located on.

I have read postings from people using the up-firing design on side walls (7.1 setup with 4 such speakers) and they spoke well of them. Guess it all depends on your room layout.

BTW I've taken to looking at the speaker setups at various local movie theaters and there are many different designs used here for surrounds. Some up-firing mounted low down, some down-firing mounted near ceiling level. I wonder what the THX spec's call for?