Lots to consider. What are you doing at the island - cooking, washing dishes, prep only, dining? The main concern for me is that it doesn't interfere with opening doors fully on any of the surrounding appliances, and that there is walk room to get to the seats even when someone is standing with the fridge door open. If you are installing appliances in the island - fridge or washer drawers - make sure they are at convenient spots. Dish washer near the cabinet where the majority of dishes will be unloaded after washing. Fridge drawer near a sink for washing fruits and veggies before cooking. If you want a regular sink elsewhere and a prep sink in the island, the one closest to the stove should have a pot filler. Hope that helps.

Very helpful, thanks! Space all around the island is not a concern - there's plenty. We'll only be prepping on it -- no major appliances or sink -- although there will be a couple of stools on the non-work side that I envision the kids sitting on for their breakfast or for doing homework. So really, my main concern is the depth of it - at what point does it become non-functional? I thought 4' sounded fine, but a friend thought it would be too hard to hand things across...

How wide is your dining table? If you can reach across it comfortably, then go for that width and no more.