Like others have said though, a barber NPC would be very useful. If there ever is a time where I want to see my character's hair change, it'd be very different, which a constantly increasing length just couldn't do for me.
And on a slightly off-topic note, I hope Bethesda creates more attractive hairstyles this time around. There were really only two or three good ones that I used often in Oblivion, and then everything else just looked outrageously awful. I'd like it if every (humanoid) race had at least 30 well designed styles to choose from, instead of about 10, 8 of which look absolutely ridiculous and the other two could use improvement.
New eye colors too...