I think Cameron will be splitting time with Ellsbury and Drew depending on the matchups. He will also be taking some ABs for Ortiz. In those cases, Drew might be the DH.
I think last season's performance against lefties was exacerbated by the fact that the top RH hitters were DL'd for big parts of the season. With the big righties out of the lineup, Drew and Ortiz were really worked over by the lefties. They never had to give in to Drew or Ortiz, because they didn't have a lot of protection behind them. In 2011, if Terry drops them in the order against lefties, they will still not have much protection behind them, but they should be batting with more runners on base in front of them than they did in 2010. That will put more pressure on the pitchers causing more mistakes.