Any cases of teaching REALLY mattering for career (tenure or otherwise)?

I do know that when applying for positions in academia most schools ask for your reviews from the courses you have taught. I think this is a case of quality over quantity with stellar reviews being the most persuasive. Knowing how fickle undergraduates can be (and just as an act of good teaching) I typically use a tool like survey monkey 1/3 or 1/2 way through the term to gage how students are feeling about the course and what they feel is lacking, etc. This allows me to address any issues before they end up set in stone as my final reviews.

Also most schools ask for a mock syllabus. These can be a challenge to write so it can be useful, when possible, to teach your own independent course, rather than just doing ta-ships. This shows that not only can you make up a course, but you can teach it too.

I've been told that getting "teaching certificates" through your school's graduate studies program is a waste of time and I tend to agree. That said, it seems like many graduate schools are putting more of an effort into actually teaching graduate students how to teach - which means that these few lines on your C.V. may become more important in the future...

Finally, it really depends on the kind of school you are applying to (where you want to end up - if you have any choice). A "Research 1" university isn't going to care much about your teaching record but will expect high volume in terms of your publishing record, while the converse is true at many liberal art colleges.

I also struggle with this--I'm not Research I material and so I know I'll end up at a place that emphasizes teaching. I wasn't getting teaching experience through my program so I (luckily) was able to teach at the local community college (just this semester). I would say that yes, you need to teach SOMETHING but I've seen job ads for my field where they specifically want people that can teach quantitative methods, for example.

A friend of mine got an interview with a small liberal arts college that said their tenure was based SOLELY on teaching.

In the end I think it may differ by field and the type of place you're applying to. (which of course, is not very helpful)

This is an interesting conversation.  I chose to keep my day job and do my doctoral program at night which means no teaching will be on my CV when I graduate.  I'm still on the fence about whether or not I want to stay in my field (still higher ed, but administrative) or go into teaching, but this is something definitely weighing on my mind.

I completely agree with everything Naomi said.  Having a little teaching experience is good for getting a job.  But there is diminishing returns in teaching a lot of classes.  Especially, a lot of different classes. 

One thing I would add both for trying to get a job but especially for advancing ones career is to document everything.  Start creating a teaching portfolio and keep adding to it.  Many schools actually have a teaching center where there are people whose job is to help you be a better teacher.  They are a great resource and will help you figure out what to include in your portfolio.  Documenting as you go along will help with annual evaluations and for promotion and tenure.