Fidelity Investments came out with a study showing that retirees need approximately eight times their last salary level to be properly prepared for retirement. For example, if one is earning $60,000 at age 65, $480,000 is the retirement base line. Frankly, I think the number eight is too low. There are a number of ways to determine what the retirement savings level should be and the Fidelity number is one.
There is a useful series of five articles on retirement over on the Portfolioist.com. I've mentioned these articles before, but if you missed that reference, here is the link to the second article. These two links will get you started reading this important series of five retirement articles.