Do multivitamins do any good as nutritional supplements?

Yes: However, a reasonable diet contains plenty of them.

Not always: Despite the hype, hoopla, and hyperbole, multivitamins serve no purpose in someone who has no nutritional deficiencies. If there is a deficiency, that specific deficiency should be addressed first by whole food sources, and if that doesn't work, only then by supplement. If you have enough of a vitamin and/or mineral, more is not better.