I think the signing can be viewed on how much they spend on him. I am reading one yr contract which sounds more than minor league contract, which is what I would have expected on this.
The sox are very right handed. Their nemesis in NY has Damon, Abreu, Giambi, Matsui, Cano and potentially Mientkiewicz in their starting lineup. Then you have Posada who has a little less pop from the right handed side as opposed to the left.
The one thing he gave last yr was that he held lefties to a .202 BAA and a .600OPS. The problem being that he faced 15% more righties than he faced lefties, and righties lambasted him to a tune of a Manny-esqe OPS (1.029). The funny thing is, 2 yrs ago, those roles were reversed, as he dominated righties and was owned by lefties.
Overall, this move depends on how much and what role he will occupy. If they want to use him like the yankees used Villone (set up man), then this is a VERY BAD MOVE. If they are going to try Okajima as a potential set-up man or at least a 1-2 inning reliever and exclusively use Romera as a lefty only pitcher, then this is a good move.