Do student reviews of teachers matter? As the title says, do student reviews of teachers actually ever matter? 

At least in the U.S most universities I know of have their students evaluate their teachers at the end of each term. I do know that things like tenure, if they do research, or if they are just an instructor plays a role in how weighted these evals are but even so, does anyone know if anyone actually cares or does anything with the reviews?

I've had many teachers of all types and some were notoriously horrible. Every year hordes of students would write lengthy reasons why the teacher was bad, give them very low marks, etc... And yet the teacher has remained. 

I do know some teachers who do actually care (the teachers get them a semester  later) and they can look at what the students liked/ disliked, etc... Which seems like the only way these evals are used. At least the way it feels to me, the administration (the ones who require these reviews), simply collect them, put them in a file, and never speak of them again.
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.