It's crazy their deals...I started buying parts from there for the past few months and on average I save about 30% per order....once I got a $50 coupon for spending $100.
My recommendations, always google Advance Auto "Coupons" when you need to order parts. There is always some amazing coupon floating around. I usually pick my items up at the store (i.e. fluids) but if you spend $75 or more on non-fluid parts, they ship for free to your house.
They also carry a few Griots products...and 40% off their products is a steal in my opinion.