I buy most of my groceries online from Tesco and I am so impressed with them. I had a few bad experiences with Sainsburys a couple of years ago, most notably when one delivery took 6 days to arrive!
I switched to Tesco and the service has been awesome. I get a slight problem with a delivery every now and then but it's usually 100% complete and on time. I got my latest delivery this morning and it was a bit screwed up. A few items were missing and, most importantly, someone in the store had substituted 2 4-pack AAA alkaline batteries for 2 4-pack rechargeable batteries! These cost £8 each so I was charged £16 for batteries that I could not use.
I called the helpline and after a couple of phone calls they refunded the cost of the missing items and the £16 for the batteries. They said I could keep the batteries! I haven't got a charger for the batteries but it's the thought that counts...
Any good stories or horror stories about your online grocery shopping?