Which way should a seat post clamp be oriented? I heard somewhere (I don't remember where) once that a seat post clamp should be oriented with the gap at the front of the seat tube, opposite of the gap in the top of the seat tube. The logic behind this was that it supposedly exerts more equal pressure around the entire seatpost. 

However, I've noticed that bikes off the rack are almost always sold the other way around, with the two gaps on top of each other.

Does it really matter? Is one way better than the other?
Typically, for an aluminum post you align the gaps. For a carbon post you turn the clamp 180 degrees from the gap in the seattube to minimize the chance of crimping the seatpost. Some manufacturers have their own recommendations, but they're typically in line with what the aforementioned guidelines.