I've been waiting for a test module like this for a while to help me keep my manifest up to date since I almost never do make manifest. It would be nice if you could tell it which directories to ignore. For example, some dists create scratch files in t/var when running tests. There's no reason to compared that directory to manifest since things in there are no permanent.
As a side note, is there any good reason why Makefile.PL has use 5.008006; in it?