Watch this video, or if you have dial-up, I'll give you a synopsis:
Ben saves 2,000 per year from the time he is 19, until he is 26 years old in a mutual fund that gives a modest 12% annual return, and then stops. Arthur begins saving at 27 and never stops until he retires. At the age of 65, Ben has retired with $2,288,990 off of a mere $16,000 of earned income. Arthur retires with $1,532,160 after saving $78,000, and he will NEVER catch up.
In the words of Dave:
"The point of this chart is not that you should have started, it's that YOU'D BETTER START!"