What say we have a thread dedicated to this little technique, everyone does it differently, so lets hear how you do it.
Personally i load two files into a photoshop stack, one colour one B&W, the B&W on top, i then erase the area i want uncovered on the B&W layer, then adjust the colour parameters of the colour layer so they match the feel of the B&W layer they penetrate onto. I know you shouldn't use the eraser as its somewhat permanent but its the only way i have figured out how to do it, if you have a better way please come and share it.
I thought i would end this post with a quick example i have done tonight.
