A friend asked me today whether I knew about iDine. Of course, I know all about it — it’s great.

Here’s how it works. It’s free. You sign up. You go to restaurants. You earn 10 miles for each dollar that you spend at restaurants that are on their list — including miles for tax and tip.

You can choose to earn miles on Alaska, American, America West, Continental, Delta, Northwest, United, or USAirways.

The whole system is automatic. You register your credit card, and the points post automatically when you pay your bill with that card.

The only limitation is that you are generally only able to earn miles at a particular restaurant once per month. However, there’s a way around this constraint… a glitch in their system. Just sign up different credit cards to earn miles with different airlines. If you register one card with United, one with Delta, and a third with Northwest you will be able to earn miles at the same restaurant three times in a month as long as you pay with a different card each time.