From day one in car audio I've heard a lot of really good setups and they have all had rear fill. Due to some maniac ramblings I've read on this site my current project has started purposely using front component speakers only. Its a whole change in mental attitude.
So far I am much more impressed with doing it this way than I thought I would be. I am getting a good full bodied sound and am thinking more and more this may be the way to go. Keep in mind I only installed some door speakers quickly and played with positioning of the tweeter. (this is no killer system by any means).
Still lots to do later but I had to get some sound going for now.