mathematics education - How seriously should a graduate student take teaching evaluations?

Positions not associated with teaching (such as industrial or government labs) will very rarely care about your teaching. When I applied for these, I didn't even bother to list my teaching on the cv.

Teaching positions (such as at a community college) will probably care about it a lot more, since they want some proof that you can teach well. But I can't say much since I don't have experience with these.

Research universities are somewhere in-between. In general, their main priority is the quality of your research. So for a standard tenure-track faculty positions, they will likely focus on selecting an interesting (research-wise) colleague rather than the best teacher.

Of course, research universities need to teach too, and they do feel the pressure to teach well. Also, "research university" is not a uniform designation; different universities will have different priorities which may include more or less emphasis on teaching.

Generally, teaching works like this at a research university. The department (math, in your case) needs to teach some courses. These are service courses to other departments (such as "calculus 1 for biology students") and internal courses (e.g. "graduate group theory"). These need to be taught adequately. If the service courses are not taught well, other departments will complain and your dean will not like it. If the internal courses are not taught well, then your colleagues will have underprepared students to deal with, and they will not like it. So people will want to know that you can teach adequately. Generally, at a research university, I would take "adequately" to mean that you will not leave the students grossly underprepared. Whether they love your teaching or not is less of an issue. So, as long as you have some teaching experience, I would say you are OK.

Now, you don't have to list ALL teaching evaluations on your cv. If the evaluations are great, mention them. If not, you can omit them and just list the course. For example:

TEACHING

Fall 2008: Calculus 1

Spring 2009: Algebra (received 4.5 / 5 evaluation)

Fall 2009: Linear algebra

...

Also, I don't think good evaluations will affect your candidacy negatively. It's true that some people might interpret interest in teaching as lack of interest in research, but I don't think good evaluations are enough for that. If you teach a lot, if you publish papers on teaching, go to teaching conferences, etc. -- in that case, yes, people might be suspicious of whether you are interested in research at all (especially if you don't have an equally active research program). But I don't think that just having good evaluations will do you any harm.