I used to work in QA and have been a proponent of unit testing generally, but I tend to agree to some extent. You can't see your blind spots, by definition, so

I used to work in QA and have been a proponent of unit testing generally, but I tend to agree to some extent. You can't see your blind spots, by definition, so you need really clever & devious testers to do the oddball test cases that you never think of. If you can find someone really good at ad hoc testing they can be quite efficient. Such people are hard to find. But I also think that certain automated frameworks/tests make life easier for everyone, if they're managed well. At a minimum, they can serve as a sort of de facto specification in cases where the system lacks adequate documentation (which is the case more often than we might like.) And as others have mentioned, unit tests serve a dual role. Even if they're not great at finding new bugs, they have some value as regression tests.