Bankrate.com has a great article complete with a chart showing how much you should be saving for retirement, taking into account what you have saved already. (In my humble opinion, these rates are too low, but a good place to start.)
I found this paragraph to be a cheerful, comforting point:
Net pre-retirement income refers to your gross salary minus the amount you're putting away for retirement. That stands to reason: After all, you're managing to live on your earnings minus retirement savings right now, and you won't be saving for retirement after you've retired. This takes some of the pressure off, since it substantially reduces how much you need to save.