After looking into Maya's Character Set and Trax animation features, it is clear to me that there is good reason for there to be so little information about them on the net. They suck. The concept is really cool and would be useful in production, but the implementation is finicky, frustrating, and has the potential to completely screw your work.
The character set creating workflow is simple enough at first, but there are a number of major problems that crop up:
Character sets interrupt how Maya stores animation curve data in relation to actual controls. If a character set is changed on the rig file, it has the potential to wipe the animation from a curve, since its curves are connected to the character set node rather than the control itself. For example, taking the structure LowerBody>Legs>LeftLeg/RightLeg and merging the lower nodes up into a single LowerBody node will wipe all animation from the controls that the lower-level nodes contained.
The Trax editor can only create clips at the lowest character level in a set with subcharacters rather than allowing you to choose the level at which the clip is created. For example, creating a clip by choosing the top node in the LowerBody>Legs>LeftLeg/RightLeg character/subcharacter hierarchy will result in between 2 and 4 clips (depending on whether or not the higher levels have controls not contained in lower levels), instead of a single LowerBody clip. EDIT: There is a way to group clips so you don't have to fiddle around as much with each individual clip, but that seems to leave more room for fiddly errors than creating a single clip at a higher level.
There doesn't seem to be any clear way to save Trax clips as external files. Defeats the purpose of creating a library of clips which can be imported into a scene as needed. EDIT: Apparently you can export the clips as MayaBinary or MayaAscii files. Doesn't rectify the more egregious issues mentioned above.
Some of these shortcomings are based solely on my own expectations, needs, and limited experience, so I admit that there are those who won't find any problems with what I've pointed out, or who can show that I don't know what I'm talking about. In any event, the tool I was expecting this to be shouldn't really be that hard to implement. It wouldn't surprise me to learn that most studios have their own scripts written to do just that. In the meantime, I'll have to find an alternative solution for segmenting and storing my animation clips.
EDIT: As these later comments show, I wasn't writing from the full picture. Even with clip grouping and exporting abilities, though, the animation-wiping nature of character set nodes is a deal-breaker for me. It's unconscionable to me for a setup artist to use a system that could potentially destroy large chunks of, if not all of, previously completed animation when updates and alterations are added.