When you floss, you help prevent your gums from becoming inflamed. That's a good thing. What is happening when your gums are inflamed is that you have a chronic bacterial infection in your mouth. This harms your arteries through two mechanisms: the bacteria find their way in to your arteries and hang out (causing plaques), and your body mounts an immune response to the bacteria in your mouth, causing inflammation (which in turn can cause your arteries to narrow). This makes it hard for your heart to do its job and can lead to heart disease.
There is some debate about how many years you can gain with heart disease. Dr. Perls says 1.5 years, while Dr. Roizen says 6 years. Both of these doctors are gerontologists (aging docs) and have popular books on aging and life expectancy (see reviews: Living To 100, RealAge and You! Staying Young). Who is right? It doesn't matter. Flossing is good for your gums and good for your heart, so we should all just do it.
Of course, this is easier said than done. How do you get in to a solid flossing habit? First, you need to make sure you have some floss. There are tons of different kinds of floss (flavored, unflavored, strings, ribbons and on and on). Pick some and give them a try. Next, you have to remember. Put your floss on top of your toothpaste. Hard to forget that way. Then just do it. You already have a habit of brushing your teeth at least twice daily (right? - please say yes), so just anchor your flossing habit to that.