All of the above comments deal with the operational aspects of delta vs. wye distribution but ignore the safety aspects.
The wye system is, by my estimation a far safer system than delta. First, the voltages (assuming the center of the wye is grounded) are entirely predictable---480V phase to phase and 277V phase to ground. With floating delta, while you will have 480V phase to phase, there is no control over phase to ground voltages. One leg could and often is accidently grounded so it will be zero volts to ground but the other two phases will be forced to 480V to ground. Or, worse, the whole network can be taken to a very high voltage to ground. I've seen 4160/480V transformers with defective or leaking insulation which produce 480V phase to phase but have the whole secondary network floating at 4160V to ground. Your maintenance people have 1000V cat IV meters but unknowingly are being exposed to much higher lethal voltages. I've seen floating networks in automotive plants floating 800VDC above ground. That, too, is not what your maintenance people are equipt to handle. And there is NO WARNING that these voltages are present!
Second, 277VAC to ground does not usually conduct thru dust unless it is very wet or is otherwise conductive. 480VAC, on the other hand, ionizes dust easily. When that happens, you can have a properly locked out, tagged out machine with the 480V to ground conductors leaking current around the disconnect thru ionized dust causing the load side conductors to float up to 480V. I had this happen to me twenty years ago on a corner-grounded 480V floating delta system and I am lucky to have lived thru the experience. That's right, a locked out and tagged out machine with 480V on the load side conductors! This would not have happened if the machine had been fed with grounded-wye 480V.
Bottom line: I believe floating 480V networks should be unlawful to install due to the safety issues. If any of you are unfortunate enough to work in a facility with this kind of power distribution, please protect yourself by adding a four-legged ground wire to your tool kit. Whenever you lock out a machine, also attach one leg of the ground strap to ground and then the remaining three to each of the load-side conductors. Only then can you be sure they are safe. I know, its a bother; but it's your life.
And, as for new construction, please, no more floating networks.