We've recently switched E to whole milk from breastmilk and I've been buying organic, just because I hadn't really had time to do my research. I was under the impression that conventional milk contained hormones that could effect him, but after doing some research that doesn't appear to be correct. The AAP has this to say:

There is no evidence of clinically relevant differences in organic and conventional milk.

a. There are few, if any, nutritional differences between organic and conventional milk. There is no evidence that any differences that may exist are clinically relevant.

b. There is no evidence that organic milk has clinically significant higher bacterial contamination levels than does conventional milk.

c. There is no evidence that conventional milk contains significantly increased amounts of bovine GH. Any bovine GH that might remain in conventional milk is not biologically active in humans because of structural differences and susceptibility to digestion in the stomach.

They also explain that Estradiol and progesterone concentrations were lower in conventional milk than in organic milk.
http://pediatrics.aappublications.org/content/130/5/e1406.full

There are definite benefits to the animal in an organic vs. non-organic setting, but there doesn't seem to be a benefit to the health of the consumer.

So, why to you choose to use/not use organic milk? I guess I'm not sure if it's really worth it.