CTR makes some good points regarding rounds. The gist of it is that any provisions for steering a round will weaken the ultimate strength of the canopy. Some designs to speed canopy openings even employ high drag devices on the rear of the canopy to decrease opening time - the exact opposite of the normal modifications used to enable steering.
An experienced canopy pilot can get some steering out of a true round(or more likely conical) parachute particularly if it has four risers but it takes skill and strength. With good timing and some luck you can even get a bit of a flare out it but if you mis-time it you'll do more harm than good.
has tested ram-air(square) parachutes for ejection seats. The results were good as I recall but I don't see them being put into operational use any time soon due more to training/psychological issues rather than any engineering issues. They're much more steerable, land much more softly, etc. but can also very easily kill you if you don't really know what you're doing.
I know that many pilots have made parachute jumps but the majority find the very concept to be distasteful. Simply put, I believe that very few pilots are willing to make parachute jumps for training purposes and it's an absolute necessity to safely use a square parachute. A lot of progress has been made over the last decade in simulators that could very well meet needs for currency training but a few real jumps up front are really necessary to get the real feel for how it works.
As an example, Strong Enterprises makes a very nice pilot's rig for jump pilots and aerobatics that has an option for a square canopy. They will not deliver it to the purchaser without a minimum of two tandem jumps IIRC.