Do student reviews of teachers matter?
Yes the reviews matter in a number of ways. They are generally considered by tenure and promotion committees and consistently awful reviews can prevent tenure/promotion even for someone with excellent research and service. Committees look both at the average/median and the spread/extremes of any numerical scaled questions as well as the open comments.

The evaluations are also used by some people to actually improve their teaching. This is obviously much harder to enforce, but in my experience no one sets out to be a consistently bad teacher.

Very rarely would a teacher be fired based on student evaluations since they have a number of inherent flaws. First the scores and comments tend to be much better in electives than required classes. Scores also tend to be better in small group teaching versus large lectures. Some topics also tend to score higher than other topics regardless of who is teaching. There is also the issue of bias. Student comments can reveal a shocking degree of sexism, racism, and homophobia. Finally, the timing is really wrong to evaluate how much the students learned and how important it was. Asking for an evaluation before the student can see how the class fits into the entire education, and future job, misses so much about what a teacher is trying to do.