I use linear algebra when I work on graphics routines. I have never worked at a graphics-oriented company, but guess who gets to skip out on CRUD work because they're the only one with the math background?

I've used discrete math and other stuff to work on optimization problems -- once again, I've worked at regular non-tech companies, but guess who gets all the fun stuff because they still remember their stuff?

Also, because it's been 10 years and I still keep up (more or less), I do pretty well with algorithm problems in interviews.

It's true though, that if you don't use it, you will lose it, and then you will probably never learn it again, so you get stuck doing really boring stuff and then say "I never use the stuff I learned."