Good student evaluations supposedly used to count against people at one research-focused university I heard about, being thought to indicate bad priorities. But at most colleges that emphasize teaching, i.e. that don't emphasize research, I would be very surprised if good teaching evaluations weren't the single most important factor in tenure decisions.
Also worth noting is this comment:
the majority of faculty are now off of the tenure track and these teachers are often evaluated only by students evaluations. This labor situation gives these faulty mechanisms incredible power and creates defensive teaching and a lack of academic freedom.