Today is the deadline for teams to offer their free agents arbitration. I would expect the Red Sox to offer all four of their top free agents arbitration. This four includes Pedro Martinez, Jason Varitek, Derek Lowe and Orlando Cabrera.
Best case for the Sox would be for all four to accept arbitration but that's not going to happen. If the Red Sox don't sign these players at least now they will get draft picks in compensation if another team signs them.
Arbitration day is important because a team may be hesitant to both pay a player a big contract and give up draft picks. Arbitration day helps set the true market for the free agents. It is also interesting to see what players are and are not offered arbitration. Not getting arbitration from your current team is like getting a huge sign that says "don't let the door hit you in the ass on the way out."