Tax-advantaged employer-sponsored retirement savings accounts hit a milestone not long ago: At least half of all private sector U.S. workers now participate in a 401(k).

That is good news in this respect: The alternative of not saving money for retirement could prove crushing. Finance experts have long cautioned against relying solely on Social Security to (inadequately) cover retirement costs, a point reinforced by Social Security’s own looming insolvency.

And fewer non-government workers are covered by pensions (about 15% of U.S. workers currently have access to any defined benefit plan, according to the Bureau of Labor Statistics). Setting aside money for retirement is practically a necessity.

Yet all is not happy and carefree in the world of tax-advantaged savings (that includes 4

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