Is The "Balanced Portfolio" Dead?

The conventional widsom among so-called investment people is to invest in a “balanced portfolio.” That means to invest in a prudent mix of stocks and bonds (such as 50/50 or 60/40) based on your personal goals and your tolerance for volatility. But over the last 5 years, the balanced portfolio has been horrible, with stocks up 100% and bonds up 0%. Why would anyone want bonds in their portfolio!?