Okay, this is coming from an AP chemistry class I took nearly three years ago in high school, so bare with me if it's got some mistakes.
Basically, the oil on your hands is made up of elements that are organically bonded, otherwise known as non-polar bonds, meaning that the tips of the molecule have no charge. Now, the number one rule when different molecule stick together to form one entity is that like attracts like. In other words, non-polar molecules will stick to non-polar molecules, and polar to polar. Which explains why water and oil don't mix, as water is a polar molecule.
Now, I'm not sure of the exact composition of acetate, but I would assume that it is mostly made up of non-polar molecules just like most normal plastics. So, the oil forms a strong bond with the surface of the acetate. Alcohol (all forms, beer included

) is made up of non-polar molecules, which explains why it is such a good tool to clean fingerprints off cels.
It probably leaves fingerprints because of the dirt mixed in with the oil on your hands. Dirt usually consists of polar molecules, but it can still form very weak bonds with non-polars. Rubbing alcohol is almost never 100% alcohol, so the water mixed in bonds with the dirt and takes it away with the oil. Alcohol breaks it's weaker bonds with water to make stronger bonds with the oil, and the dirt breaks away for the water. Stronger bonds=more stability, so this occurs quite naturally in nature. Soap works in much the same way when you wash your hands. It is mostly a non-polar molecule with a polar "tail" to attract both dirt and oil, which bond and then rinse away in water.
But, paint is also mostly non-polar molecules, so alcohol will dissolve it as well. If I made any mistakes here, feel free to correct. It's been a while, but these are some basic concepts in chemistry, so I think I got them all right.
But . . . even knowing all that, I don't wear gloves.

I really should, and have been meaning to buy some. Honestly, I think some people would freak if they saw me handling my cels when I first get them. After a pass under the scanner and a quick cleaning, they're stored in bags and books, and I don't take them out again. Despite all of the warnings dished out, the only problems I've ever had was once with some airbrushing, but I learned my lesson there. Airbrushed cels are now treated like the original Mona Lisa in my hands.
