I had to take such a formal proofs course too, just with a different tool that had even steeper learning curve and rough edges (prof used us as alpha tester of

I had to take such a formal proofs course too, just with a different tool that had even steeper learning curve and rough edges (prof used us as alpha tester of his new tool), and came to the same conclusion as you. It seems very valuable to formal proof specific small sub-sets or rather critical components like device drivers, like e.g. Microsoft is doing it for some time. I am sure it will become more popular, when the tools and languages get more mature and easier to grasp for average joe developers in the next years.