I'm a DINK: Dual-income, no kids.
My wife and I both max out each of our 401ks. We way oversave, but we don't really need the money now. And I'd rather save now while we can then to ever have to worry about money in the future. Plus the flexibility of having most of the investments in a tax-deferred plan is a real benefit when trying to achieve a proper mix of investments (rebalancing in a tax-deferred account is not a taxable event, rebalancing in a taxable account triggers taxes and an accounting nightmare).
That said, we also have taxable investment accounts for the massive tax savings that come along with those for those in the know (i.e., donate shares instead of donate cash to charity). Taxable investments are only taxable when you get dividends or sell the shares. Invest in items that you never intend to sell and focus on having the minimum dividends in the taxable account. But that only really works well when you can heavilly invest in dividend paying stocks in tax-deferred accounts.