Sean, I'm glad you mentioned this because I thought everyone here shaved their head for practicality.
I've got huge hair, and it's a pain in the butt when backpacking or climbing. I've had big bulky dreadlocks for seven years, and even when trimmed short (chin length... they were waist length at one point) it is nearly impossible for me to wear hoods (rain jackets!) or hats (my filson sun hat is size XXL and fits quite tight), and my hair is always getting caught in pack straps. The bottom line... long hair really isn't practical for any outdoorsy pursuits.
On a similar note, how about beards? Guys? Anybody else have huge facial hair that gets in the way of backpacking?