An earlier post mentioned TrackerViz, a free script to work with tracking data that lets you animate masks using expressions and "average tracks together, correct drifting tracks, use averaged tracks to calculate rotation and scale, and it's the simplest, easiest way to apply tracking data to mask vertices EVER for After Effects!"
Now Mathias Möhl adds 2 scripts for tracking and masks, which can be used in combination with TrackerViz: KeyTweak and Tracker2Mask. There are also videos explaining them; here they have fullscreen controls, but you can get the HD versions if you watch at Vimeo.
Tracker2Mask allows for local modifications of masks and computes the movement of mask shapes based on the movement of track points so you won't need one track point for each mask point. An earlier tutorial explains the basics and shows how to animate speech bubbles. The 2nd tutorial shows how to rotoscope the shape of a moving car based on only four track points, though for simpler shapes often one track point is sufficient:
The other script by Mathias, KeyTweak, lets you quickly modify any keyframed property. You can modify a few keyframes by hand and KeyTweak will modify the keyframes in-between accordingly, to help modify drifting tracks, correct rotoscoping errors, or make non-uniform mask expansions. Like ones made using TrackerViz and Tracker2Mask. Here's the tutorial:
In a similar vein, recent videos by Aharon Rabinowitz might come in handy: Super Tight Junk Mattes (using Auto-Trace to refine garbage mattes) and RGTV Episode 4: Better Compositing Techniques (which leverages convenient Red Giant filters).
Update: Responding to a roto question Patrick Siemer and Chris Meyer mentioned these scripts later the same day on the AE-List, and pointed to further discussion and comparison on the AE Enhancers script forum; see Tracker2Mask: new tracker-assisted rotoscoping tool.