I use this program as well. One really good way to boost your points if you're with a group at a participating restaurant is to be the money collector for the bill, hold the cash, and then pay the entire bill through your own credit card. Of course, you have to be disciplined and use the money to pay the credit card charge at the end of the billing cycle, but if you're on the 5-miles-per-dine level, you can easily earn 1000-2000 miles for one dinner to which you contributed no more than $50-100. I've done this a number of times, including once on a triple bonus promotion that netted me well north of 2000 miles.

And even if you don't use the program frequently, it's a really great way to keep your miles from expiring since a charge through this program counts as mileage activity.