TrackerViz, a free script to work with tracking data

Update: the new home for TrackerViz is AE Scripts.

Via AE Freemart, AE Enhancers hosts TrackerViz, a free script from NAB Scripts that makes it easy to work with tracking data. Matt Silverman and Lloyd Alvarez are fans; you can 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!"

There's also Quicktime movies by Sean Kennedy explaining how to use TrackerViz. The first part quickly goes over the After Effects tracker to explain the settings you might want to adjust. The second part shows how TrackerViz can tweak, modify, and correct tracking data. The third part shows how to use the tracks to create an instant roto.

Update: Last year Sean Kennedy also discussed Using tracks to help roto, mimicking Planar tracking and Demoing ALL the options for roto tools for newbies.

Update: Check out KeyTweak and Tracker2Mask: scripts with tutorials based on comments below.