I've noticed the free shipping is usually on Sunday--I get the daily special alert in my email so I know what's on special everyday. And yes it's usually on $50 order. This is when I order those heavy items!
I was going to take advantage of the 10 percent discount "today only" sale, but I will wait for free shipping, as it was more than the discount. Bummer, I thought it was ALWAYS on if you spent over $100, which I was going to do, but I won't pay shipping AND spend that much! They should have free s/h all the time over $100!