Servant or Slave?

For its Bible study, my church is going through John's Gospel: Wisdom from Ephesus, with Michael Card.

Last night, the group was talking about whether Jesus was a servant or a slave.  Michael Card, if I recall correctly, was saying on the DVD that Jesus was like a slave when he was washing the disciples' feet.  But some of the people in the group had problems with calling Jesus a slave, preferring instead to call Jesus a servant.  For one, a slave does whatever his master tells him, but Jesus is not bound by our orders.  (Still, someone in the group noted that Jesus obeyed his Father.)  Second, one person was saying that a slave obeys because he has to, whereas a servant helps others because he wants to.

I thought these were good points.  I doubt that they hold up in the Greek, for, when Jesus is said in Philippians 2:7 to have taken the form of a servant, the Greek word there is doulos, which often means a slave (see here).  One could perhaps say that Jesus is not completely a slave, but that the metaphor still holds some water because Jesus, like a slave, serves.  Or perhaps one could say that Jesus being a servant is voluntary on his part. 

What's important, of course, is what someone in the group said: Many people tend to ask what they can get out of something rather than what they can give.  I know that's true of me.  And that is one reason that I go to church and Bible study: to be reminded of a better way, and to interrupt my selfish thought-patterns.