Melky has basically secured the leadoff spot coming out of spring training for the days he'll be playing - so much so that he may be playing every day between left and center. He ripped it up and McLouth struggled and now has the injury too. I wouldn't be surprised either if Glaus bats 4th some, depending on the pitcher. He's really the key to the entire season, IMO. Also, Medlen is the only other "long" option if someone in the rotation goes down.
Also, not having a single lefty in the rotation is crazy. None of the guys really over-rely on breaking pitches, but hopefully that doesn't hurt us in the long run.