Ask HN: Should I validate my HTML?
As an aside, HN has quite a few validation errors: http://validator.w3.org/check?uri=https%3A%2F%2Fnews.ycombinator.com&charset=%28detect+automatically%29&doctype=Inline&group=0&user-agent=W3C_Validator%2F1.3+http%3A%2F%2Fvalidator.w3.org%2Fservices