Last night I watched the instructional DVDs, Eddie Reese on Butterfly and David Marsh's Swimming faster butterfly. Both had different takes on how to do a proper pull and sweep. (The above links have movie clip samples)
Eddie Reese of the University of Texas, Olympic team coach for many Olympics said that the arms come out at shoulder width and began there sweep just under the neck so close that your thumbs nearly touch. David Marsh of Auburn stated that the pull sweeps underneath your belly-button and then sweep out as if you were emulating an hour glass shape. I talked to Anthony this morning and he said that the Richard Quick DVD; (Richard Quick coaches at Stanford), also endorsed the sweep in and sweep in and sweep out as the coaches above.
But Ian Crocker goes his own way. His elbows are high and he practically sweeps straight on through with only a wobble.