My friend Michelle just sent me this article from Slate about the environmental impact of cheese. Interesting topic. Two quick take-aways: Sheep are gassier than cows or goats. Soft cheeses are better for the environment than hard cheeses (due to higher yields and lower energy needs for processing and aging).
One blatant omission, though: The article doesn't say anything about how far the cheese needs to travel to reach your plate. Buying local makes a big difference... and making your own cheese at home is as local as you can get! (Gotta use locally-produced milk, of course).