I have been using On1 for about 3 months and the more I use it the more I realize what a versatile program it is. I am using it more than Photoshop and loving the results. In addition to the program On1 has a great tutorial library in On1 University. I just looked at this tutorial on masking and found it easy to follow and more important to me I could actually do it.
On1 has a free offer (I hope it is still on) On1 version 9.0
Have a look