Well yes, that and dig out low throws, stretch to try to save high or wide throws, learn when to cover and when to field and count on the pitcher to cover, learn to field much better than he did at 3rd, hold on runners, know when to go right to 2nd and wait for a relay, etc. We widely assume that Braun will end up at 1st, but we can't just assume good defense for a guy who has not played a single inning at any level in his professional career at 1st. He could make the transition, or he might be a butcher.