I have used them 2-3 times and they are very reliable. I think there is a min order of $40-50 and a $12 delivery fee, plus an option to tip - which I do because I order a lot of heavy stuff.
You can order well before your trip...which is good to lock in a delivery slot on your date (they can only do so many per day) and they will deliver to your WDW hotel. If you pay by cc, you don't even need to be here -- they will leave your items w/Bell services, who will store things that need to be refrigerated in giant refrigerated cases, so no worries. Then Bell Services will deliver, and you have the opportunity to tip again!!! I usually order milk, case of water, juice boxes, gatorade, fruit, yogurt, bread, bagels, donuts,cream cheese, etc. You just have to make sure you don't go overboardand the fridge in your room can hold all of the items that need to be refrigerated.
Others on these boards swear by wegoshop.com .... check them out if you think it would work for your family. I think the convenience is well worth the price, especially on vacation.