From my experience (at a high-volume residency program), the learning curve is very steep- and first year residents routinely put in crazy hours when you factor in reading. Pretty much everyone NEEDS to read, just to get the BASICS of what's going on. Every time you start a new rotation you know basically NOTHING about the subject matter, meaning you are continually reading about it when you start, whether you read along with your cases or preemptively. Second year residents start to relax a bit. I hardly could bring myself to read, except for a case-by-case basis, because I felt I had a basic grasp of what was going on. I would get home after work and do anything but pick up a text book. I bought a PS3. Those who continued to read definitely had a significant advantage on pimping sessions, and probably for the boards. Now in my 3rd year, I will start reading daily again to catch up.
Hope that helps.