I agree with Ken that unit testing is part of software development.
About the cost question, it's true than writing the code plus the unit test is longer than writing just the code. However, when you write the code along with its tests - which is called TDD - Test-Driven Development, you end with "clean code that works". When you just write the code, then you have to make it work, which can be long and painful.
Another benefit is that you know where you are, as the code that has been written has already been unit-tested.
To answer your question, yes, I'm using unit testing on my projects when it's possible. I write unit tests for all the new code and I strive to for legacy code.
