FreshDirect is an online grocery store that delivers in the NYC area. I needed to do an order this morning, so I downloaded their iPhone app on my iPad and discovered that grocery shopping is one of those things that the iPad is *perfect* for (an it would be more perfect with a native iPad app). You just take the thing into the kitchen with you, rummage through the cabinets & fridge, and add what you need to your FD shopping cart. Then you take the it with you around the rest of the house (the bathroom, the garage, the pantry in the basement) adding needed supplies as you go. It inverts the usual “wander around the grocery store searching for items” shopping practice; instead you wander about the house looking for what you need.
Obviously the iPhone would work for this as well, but a tablet-sized device is generally better at these sorts of tasks: activities where your attention is shifted back and forth between the screen and something else (or shared between two people). The iPhone is a greedy little thing; it’s better for tasks that require your full attention on the screen.