honestly, i had hair down to my knees when i started biking, but turning, the grit, the wind resistance, etc, it just dragged me down so i keep my hair short ( just under chin) but if you HAVE to have your ponytail, just ties it at the nape of your neck and it's all good. i take you are mtn bike with Influx, but if not, get the bell phi, that wraparound plastic in the back is a hell of a life saver, literally... i was knock unconscious by a pretty bad crash with my influx because it's just foam in the back and cracked upon inpact
i had a similar accident recently with my new phi and the extra bit of plastic kept the helmet from craking, and me conscious. (btw, i am not a klutz or anything,... i ride in NYC traffic :S accidents happen)