We've had a couple common squirrels. One we found in our garage one day, the other was given to us, both were babies. As they get older, they start to become more wild and will bite. Its cute at first because they don't bite hard enough to break the skin or cause any pain, but then a few weeks later - BAM - they start nailing you hard for no apparent reason.
That and they will climb all over you like a tree. This isn't as neat as it sounds, because they have claws, which they use to dig into you through your clothing while they are scurrying around on you.