When I read that Sigmund has a plastic fetish I just had to write to you. My cat had the same addiction and it turned out it was a sign of acid reflux. Beyli would lick and lick the plastic and then often throw up. There is oil on plastic (ie. plastic bags) in order that the bags, when placed in boxes and sent to stores, will not stick together. Beyli was trying to get rid of the acid taste in his mouth and often, after licking the plastic, he would throw up. It turned out he also had the beginnings of Chronic Renal Failure, which was unfortunately overlooked by 3 vets even after bloodtests were taken. It is usually a sign of a lack of something or a problem with something that causes a cat to do this but some vets will just look at us like we're crazy . Our cats are very smart and have reasons behind what they do. Here is what I found on a website:

http://www.xmission.com/~emailbox/whycat.htm

Why does a cat lick photographs or plastic bags?
It has been speculated that they are tasting the slight "odor" that emanates from these products. They may also enjoy the texture of the items on their tongue.