It various greatly from family to family based on what you earn, what you spend, and what your expectations are for after retirement.
The best thing to do is to go to
http://www.choosetosave.org/ and use the ballpark estimator. Put in your actual numbers for what you earn, what you spend and what you expect to spend post-retirement (a common decrease in spending is that your mortgage is often paid off before retirement), what you currently have, what your current retirement savings rate is and it will help you figure out how much you need to save per year, to get where you want to be.
Everyone else can just give you rules of thumb, but not actual targeted advice on what will work for you. You really need to plug in your own numbers.