I did my first two today, and I would sign up for more in a heartbeat. I'd never seen them posted before until this past week.
Basically what you do is look for items in the (grocery) store that are on your list and then see if they have a tag below them attached to the shelf. My tags were supposed to say things like "Save $1.00 on your next order" if you buy so many of a particular item. Since I'd never done one before it took me about a half hour to go through the store but the report takes no time at all.
I'd recommend them if you can find them.