My hair hangs at about my waist when its loose. I just put it up in a braid for classes or work. Braid maybe goes to just past the middle of my back. So far I've never really had any problems with it getting stepped on or pulled. It has occasionally gotten kneeled on during pins but never really enough to be a bother and I have told my partners not to worry about grabbing it if they happen to. I mean honestly in real life if someone grabbed me they would not be careful of my hair, they would use it so I may as well learn to deal with it in the dojo right?
I have worn it in just a low pony tail a few times. High pony tails are no fun to roll over. Personally I prefer not to train that way just because when I sweat my hair winds up stuck to my face or wrapped around my neck...