Last night I attempted a round of DDR while wearing my KSO's. At first, there are a number of things which take some adjusting to. Since there is basically no shoe sole, the timing of the note hits is slightly later. This is due to it taking less time to move my foot and depress the direction arrow. I'm still not sure if this makes the hit timing closer or further away from the actual beats in the music, since I was playing on a new machine. Next week, I'll try again on a machine I am well-acquainted with (the DDR X machine at 仙台駅 Taito Station).
Another change that I noticed (again, may just be machine peculiarities) is that I have to push down fairly hard on the floor buttons in order for them to register in the correct instant. If I step lightly like I normally would while wearing FiveFingers, the pad hits register late or not at all. I think this is just engineering by the pad designers to compensate for people wearing heavy shoes (and slamming the pad way too hard).