Diving without a pony tail braid and some sort of hair cap is rather thoroughly annoying to me. I go with a two-pronged approach, myself. Most importantly, *always* (and I do mean *always*) dive with a braided ponytail. (I spent most of a night working an nest out of my head once, and that was enough.)
The other part is always dive with a head covering. If it's cold water, I dive with a nice, thick hood. For warm water, I use the
cheapest beanie I could find ($15 at Scuba.com). It doesn't feel a bit hot or heavy, and it's completely un-hood-like in that there's no restriction at all. Most usefully, it keeps what hair is not in the ponytail braid out of my face. (It also protects the ears if there are cute little man-eating fishies out there. :biggrin
If even that was just too much, there's always the foodservice-and-bank-robbery concept. Either use a tight-fitting hair net or some nylons-type material (like those head socks that NFL players sometimes wear under their helmets).
(By the way, if you haven't seen me in person or in photos, when I let my hair down, it's about waist length or possibly a bit longer. I imagine that's long enough to classify myself as one of those long hairs. :biggrin