Each semester, the physics department at UW-Madison has the students in each section fill out an anonymous evaluation form about their professor, their TA and the class in general. After the semester is over and grades are turned in, they give each TA a typed copy of the student's comments (not all of which are strictly about the TA's performance), and some statistics for the questions like, "On a scale of 1 to 5, how clearly did your TA speak?" Generally, the statistics don't tell you much (they might if the students could agree on what grade of clarity rates a 4), but the comments are worth paying attention to. (Professors, incidentally, get to see the original, holograph comments; I'd probably have written different things on the evaluations I filled out myself if I'd known that earlier.)
After my first semester teaching I was actually somewhat irked by the comments, so I put them on-line. (No, I don't understand that either, I just did it.) My friends thought this was amusing. My second semester, the comments were so bad, and so deservedly bad, that I was shocked into changing the way I taught quite a bit. I still don't have the heart to put them on-line, though. Ever since, I've put each semester's comments on-line as I get them.
I have no idea if these have ever been of any use to any of my potential or actual students, but, as I said, they've amused people, and even inspired others to put their own evaluations on-line.