I've been using the Rotobrush in CS5 which I have found fantastic!
I did 10 seconds of footage using 1 "span" but now I've finished it I need to go back and just tweak a couple of the frames, but when I do it starts analyzing all the frames from the start again. How can I just tweak individual frames?
I do this when using the rotobrush:
1. I let the rotobrush run with adjustments as I go using the rotobrush tool.
2. I freeze the rotobrush tool.
3. I turn on quickmask (the default is a red overlay displaying the mask).
4. I use the normal brush tool set to alpha only and per-frame and using black and white (black for mask, white to reveal) I paint my adjustments on frames that need them.
5. On the rotobrush effect layer, I turn down all mask refinement settings to off or zero.
6. I add the "refine mask" effect on the layer and adjust as needed. This way it refines the mask that is comprised of the rotobrush and my manual adjustments; it helps get rid of per-frame jutter from manual adjustments.