I don't know a lot about formal verification, but:

> So you can formally prove that your e-commerce refund management logic is correct, except for proving that you /processed the refund/. You can't even prove anything about recording the refund in your database, say nothing of proving anything about your interactions with your payment processor.

You could say the same thing about the viability of functional programming on a CRUD webapp, but languages like clojure have been used to great effect here. The fact that thera are important, even fundamental, bits that you cannot verify, doesn't take out value from the fact that you can eliminate whole dimensions of issues.