Most of the time I cannot tell who makes what comments, although once and awhile they give themselves away.
One unfortunate last year said I was “very lazy” and then proceeded to suggest that I should give them a sheet with all the formulas explaining them at the beginning of the semester. (Shouldn’t he do that himself?). Rather ignoring the fact that it took me all semester to explain all the formulas! Not exactly something I could do in one day. Anyway, from his other comments it was pretty obvious who wrote it.
But most of the comments are pretty generic and you can’t really tell. I do assume that students who are doing well are going to make more positive comments than students who are failing, who sometimes try to take out their frustration on the professor.