Though HSAs still represent a small part of the market, they are growing substantially. In January of 2007, 4.5 million Americans were enrolled in an HSA. That's up 1.3 million (or 40 percent) from the year before.

This information comes from a survey conducted by America's Health Insurance Plans (see the survey, PDF form, here).

(Thanks to the Heritage Foundation and "Friends of ATR" for the tip.)