Organic Gardening reported on some studies a few years ago that are consistent with what others have posted or linked to - that water is sufficient to wash off surface insecticides, pesticides and feritilizer from the skins of above ground crops.

I peel most root crops, even if they are organic, since they are much more likely to have incorporated whatever they are treated or fertilized with intothe skin.   I don't peel potatoes in order not to lose the substantial nutrients in the peels, but I never buy inorganic potatoes. With organic potatoes, the cost/benefit analysis suggests the benefits of of eating the peel outweigh the costs.