"Peanuts: Feeding shelled unsalted peanuts isn't messy and they are highly nutritious for the birds that can eat them. Most birds can shell whole (unshelled) peanuts, with varying degrees of effort. Squirrels love peanuts. However, don't feed RAW peanuts to squirrels and other animals because it can seriously hurt them. Raw peanuts and other legumes contain a trypsin inhibitor or substance that inhibits or prevents the pancreas from producing trypsin, an
enzyme essential for the absorption of protein by the intestine. Squirrels fed a steady diet of raw peanuts, soybeans. other legumes, and sweet potatoes could easily develop severe malnutrition. According to the Washington State Cooperative Extension Service, roasting hulled raw peanuts for 20 to 30 minutes at 300 degrees Fahrenheit, stirring them frequently, will destroy the trypsin inhibitor and render them suitable for feed. If that sounds like a lot of work, buy roasted peanuts but be sure they aren't salted. (Salted nuts of any kind should never be fed to wild animals.) "
from
http://www.avianweb.com/feedingwildbirds.html
(I feed peanuts too but I buy mine unsalted roasted from the bulk grocery store bins.) Please note that the above quote is meant to be for wild birds.