We use them all the time. We love not having to go to the store for groceries. We do tip the delivery person about $5 even though they charge an additional delivery charge, but that's because they have to haul everything up 3 flights of stairs. We've made changes to our order with not problem & we've never had an order mixed up. Sometimes, an item we've ordered will be out of stock, but it's not that much of a hassle to pick up one or two things as it would be to pick up $100+ of groceries. Besides, they pick up the orders at the stores so going there wouldn't solve that problem anyway.
We find that ordering our groceries online saves us money since we don't have the impulse buys like we did when we went to the store. Plus, I believe you can still use your Stop & Shop card & coupons. They save your previous orders so it's pretty quick & easy to place one.
We had an order scheduled when I came down with food poisoning last year. They were very accommodating about rescheduling so my BF could take me to the ER. I don't think they charged us a restocking fee either.