Uncovered Raw Meat or Milk in Fridge I believe the harm in leaving raw meat uncovered in the fridge is that more bacteria will enter, more oxygen will enter (causing faster bacteria multiplication), and more water will escape (causing dryness which probably slows bacteria multiplication, but toughens the meat, so let's consider dryness to be bad; I'm not making beef jerky).  Please ignore the stinky odors that escape; just consider the quality of that one uncovered piece of meat after we eventually cook it.

How much faster will the food spoil (percentage, compared to the same meat wrapped in plastic wrap)?  I imagine that meat with skin, like a whole chicken, is not effected as much as meat without skin, like a bare chicken breast, and that ground meat would be effected the most.  I wish I had some data to convince my roommate to cover his meat; is there any research on this?  Feel free to answer this for milk instead if there is more research for it.
There is no practical difference in spoilage time for wrapped versus unwrapped.  Spoilage is a factor pretty much of temperature, since in practice, all foods have pathogens present which can breed.

Assuming your refrigerator is free of insects, dogs and similar macro-fauna, wrapping is to prevent odors from going from one food to another, drying, or cross-contamination of one food by another through drips or splashing.  Now, outside of a refrigerator, where ants, flies, and so on are abundant, wrapping also provides a physical barrier to prevent infestation, but the body of the refrigerator already does that.

In fact, in some rare occasions, you may wish to specifically refrigerate your meat unwrapped:  for example, after brining a turkey, refrigerating it for 24 hours unwrapped will permit the skin to dry out, and permit a more crispy result.