I've been following this thread for some time now. I've tried the demos on some of the plugins suggested, and for the most part, they're about as good as they can be, given the circumstances.
As you well know, some of what's trying to be done is virtually impossible given the fact that some strands of hair your trying to retain are less than a pixel thick, we can only work with a pixel. Second, the color density of the hair(s) may be only a point or two lighter or darker than what you're extracting from. I've been dealing with this issue from the time we made knock-out or outline masks with amberlith and an exacto knife.
I did come up with a solution some time ago. The philosophy of the solution is 'how important are THOSE hairs, in particular. Can they be replaced by 'other' hairs that will give the final photo the same look? If the client is made to understand the difficulty of a perfect extraction and can be convinced that there is another way to accomplish the look they want, Ive found that they'll usually buy into it.
I began compiling a collection of brushes that I either made or got from others, that made decent hair brushes. I also have a collection of hair textures and colors. Curly, kinky,straight, flowing, windblown. Platinum blond to ebony black. If anyone is interested, I'll post a tutorial as to how to implement fairly easy techniques that will give you the hair you're looking for.
If this is simply an exercise in trying to do the impossible just for bragging rights then you probably don't care. But if this is about getting a good job done within the deadline and not wasting valuable time screwin' around with extraction techniques, the tute could interest you. Let me know