The human ear is quite poor at detecting the directional source of low frequency signals. So you can put a sub in your boot, and especially with some signal tinkering (phase and time alignment in particular) you can bring the sub 'forward'.
Our ears are very good at determining the location of higher frequency sounds, and this locational information is used by our brain to determine a lot of stuff about the source of the sound.
For example, if you listen very, very carefully to a well recorded track on good equipment you should be able to place the individual instruments/artists on the stage.
When you put components in the rear, particularly with the tweeter seperated and up high compared to the woofer, you can get some very, very curious effects, psychoacoustically. When you hear the exact same sound from in front of you, then a very small moment (path length difference) later from behind you, it basically makes your brain think you're in a very small room and you're hearing a reflection from behind you, or that there's 2 identical noise sources, which is very very rare in nature, and confuses the brain. It will just about make you feel like you're sitting in the middle of the performers.
Interestingly enough this is pretty much how most nightclubs have their sound setup, with speakers in all 4 corners with messed up path lengths, so if you're after club-ish (read: crappy) sound, then the same speakers at all 4 corners is probably the go.
If you want more of a concert style sound, or live performance, then good speakers up front with low-passed or no speakers in the back is the way to go.