I have plenty of them, so did my mom, so does my dad, and I've met plenty of people with them. Here are some links that can tell you more.

http://webmd.lycos.com/content/asset/adam_disease_skin_tags, http://www.merck.com/pubs/mmanual/section10/chapter125/125d.htm,  http://www.skinsite.com/info_skintags.htm, http://www.intelihealth.com/IH/ihtIH/WSIHW000/9339/10720.html, http://www.nlm.nih.gov/medlineplus/ency/article/000848.htm.

To sum it up, they are harmless.