thats a real solid rule of thumb actually, props. my last 10 or so interviews have been at accounting firms, banks, and other financial institutions. just a jacket is underdressing for those..
but, jacket and jeans, with a grey t-shirt.. casual.
jacket with a polo and jeans, business casual.
jacket, shirt, no tie. business casual +
suit.. business attire.
the jacket is very versatile, and shows you care about your appearance. I'm a fan.