Carl,
I use Mask Pro. I assume you have watched the free videos on the OnOne site and they do a pretty good job of masking hair in their tutorial, but they have a pretty high contrast background to work from. Sometimes MP can do a good job, other times not. Learning curve on Mask Pro can be steep to be effective on stuff like hair.
I've recently said in another thread, that masking hair is probably the most tedious task you can do in Photoshop. Even with high key backgrounds, whispy hair is tedious.
Russell Brown has an excellent tutorial on masking hair using channels.