I asked the same question several months ago. Short answer is there are two sides to this concept. From what I've heard, its ok with the right plastic. Believe it or not, most plastics are permeable, meaning they breath and cause oxidation at a very slow rate. I've been told that it actually can help your wine if you are drinking it within a year, but longer then that "could" cause excess oxidation. There is also a debate if plastics can leach out certain chemicals over time, but I dont know much about this, and it seems if it were that bad, you would hear a little more on it.