Poinsettia plants were once thought to be very poisonous. Contrary to earlier beliefs, poinsettias are safe to have in the home during the holidays. Most ingestions of a leaf or two has not resulted in significant symptoms. Poinsettia plants have a mild irritant which can cause nausea, vomiting, diarrhea. The milky sap from the flower may cause skin irritation.
For more information dial the North Dakota State Poison Help Line 1-800-222-1222 (Voice/TTY) 24 hours a day • 7 days a week • confidential • free of charge
You can also find an extended list of plants and thier general safety by clicking the following link: http://www.ndpoison.org/ndpoison/pdfs/plant_guide.pdf
Further, According to the ASPCA in their list of toxic plants:
... [P]oinsettias are in actuality not the deadly flowers that popular legend has made them out to be. These striking plants (Euphorbia pulcherrima) are part of a family of plants known as spurges. During the 1820s Joel Robert Poinsett, the U.S. Ambassador to Mexico, first brought poinsettias to the U.S. from a Mexican city he had visited. The myth of the plant’s toxicity began in the early part of the 20th century when the two-year-old child of a U.S. Army officer was alleged to have died from consuming a poinsettia leaf.
As a result of this rumor, the toxic potential of poinsettia has become highly exaggerated. In reality, poinsettia ingestions typically produce only mild to moderate gastrointestinal tract irritation, which may include drooling, vomiting and/or diarrhea. Keeping this plant out of the reach of your pet to avoid stomach upset is still a good idea, but you need not banish the poinsettia from your home for fear of a fatal exposure.
For more information click: http://www.aspca.org/pet-care/ask-the-expert/ask-the-expert-poison-control/poinsettia.html