I'm never sure about this question because some people count the "Grocery savings" as coupon savings, which to me, they're not. (To me, whatever the bottom of the grocery receipt claims I saved by shopping there is just advertising, not real savings.)
But, just in grocery coupons, and not including coupons for dept. stores or BB&B, I save about $5-10/trip, or about 5-10% of my grocery bill. I saved more at the beginning when I was stocking up and so could order a dozen of the same coupon to help me with the stock-ups. But it's not productive to order just a few coupons, and I don't need a lot of anything else now, I'm stocked up. Plus, I am not a good couponer, so now I primarily use the coupons that are sent to me (by Target and Kroger and different baby brands), printable ones for Target, or the ones I spot in-store (blinkies or ones on the box). I also am primarily buying fresh produce right now, and there are coupons for that, but not as many, so it's more a question of when the opportunity knocks, I try to take it.