I run anywhere from 25-30 miles/week, and I haven't noticed bulky calk muscles at all. In fact, since I've been running, bulkiness in general is disappearing. I've lost an additional 15 pounds in about a month and a half, eating just about anything I want (yesterday I had cookie dough ice cream and KFC for dinnner!-Was down another pounds this morning.)
Regardless, running is only good for your body in terms of fat loss and lean legs.