If you are early on in your career, say your 20's or early 30's and you are starting to develop your retirement savings strategy, the opportunity of a lifetime may just have materialized for you! A bear market...
The thing about retirement savings, 401(k)'s, IRAs and their ilk is that you only draw down on your savings in... retirement. And in your case, retirement is decades away, while all the stocks you will be buying just went on a very big sale (and may even go on clearance in the near future).
Yes, the market is down, but if your investment horizon is truly far in the future, that is completely irrelevant for you. When thinking how to allocate your savings, don't worry about what your stocks may do tomorrow, next year or even five years from now. All you need to care about is the very long term.
The bottom line is that if I were now starting to plan my retirement savings strategy, I would go pretty aggressive and put 100% of my money in stocks - at least for the first few years. Even now, although I am 37, my investment horizon is still far in the future. I don't plan to retire until I am about 60 and so my investment stance is still very aggressive. My 401(k) asset allocation is 80% stocks (of which approximately 50% are international stocks), 10% real estate and 10% bonds.
What I am trying to say is: rejoice young folk! The stock market is on sale! Come in droves and bring your friends! You'll thank yourselves later.