1. "We're making a mint on your 401(k) — even if you're not." The number of 401(k) investors has soared in the past decade, to nearly 50 million from 28 million, according to Cerulli Associates. That torrid growth has created impressive efficiencies for the folks who run your plan. But it doesn't mean those savings show up in your account; in fact, they could be coming straight out of it. In a practice known as revenue sharing, providers get a cut of the expense ratio on the funds in your 401(k) to cover day-to-day "administrative costs." Since the fee is...