I've found it really useful too, but I think how much it helps probably depends on what kinds of things you buy, how much time you have to keep track of the sales on your own, and maybe how brand loyal you are too. I was the type of person that bought all generic products, etc., went to the store with the lowest prices on meat, foods, etc., and I am spending much less doing it this way, so it is working for me.
It's a big timesaver and money saver-- it helps me keep track of when the things that I keep on hand (meat, baking products, yogurt etc.) are at their lowest price, for example, and I stock up. So, I'm spending less and ending up with the same or more food. We don't buy a whole lot of prepackaged foods (although I will get a few for the kids and have a weakness for ice cream myself, so will stock up on that when it comes around

). However, I won't buy anything with high fructose corn syrup or hydrogenated fats, so I just don't buy a lot of the stuff that comes up on the list. But, overall I find the list saves me $ and time. With 4 kids and working part-time,etc., I had a hard time keeping track of the sales and which ones match coupons I have on my own, but it's not necessarily anything I couldn't do on my own if I had more time.
The other thing that it is really helpful for is saving $ on health and beauty products -- 2 of my kids are teenage girls, so it helps to save $ on the makeup, hair stuff they want, etc., so they get what they like and with the combination of coupons and buying on sale I'm still saving $ over a generic brand, etc. Also, for some reason, I'm saving tons of $ on toothpaste, getting most tubes close to free. Again, it would be possible to do this on my own with more time and effort, but for me its much more cost effective to let the grocery game do it. Plus, it's fun for me!