It really is case dependent, Ie: tight shot? medium? lighting? how bad? How much motion? I have had good luck pulling a key based on the area of skin, garbage masking (and tracking the mask), then add a slight gaussian blur (you can use the transparency to control amount over base layer too). You can also move your FRONT axis in ACTION to use a "different part of the face" (once again, scene dependent). The addition of some color correction could be helpful too. I try not to roto multiple frames, as I find it's almost impossible to avoid animating paint strokes (you know, when you play it back and it "dances" all over the place), but I suck at painting. I might try to paint 1 frame to use as a element though (degrain & regrain if need be).
Obviously, SD is much more forgiving than HD. Obviously, remove any pulldown ( if source is NTSC or 1080i), because you want to work without any 3/2PD, if 1080P, no worries. I too would like to hear from other artist to get some ideas. Anyone use a Spark to help out the process?????
Good Luck! -Tom T. ( BTW......are you done yet :-0 )