I think he likes it. Since that first time, he's asked before every service if he was serving in the altar again. He wasn't actually scheduled until next month, but we did manage to get him a walk-on this week. They don't really do formal substitutions. If someone doesn't show up (on time), they just grab someone to fill in. Since he wanted to serve, we made sure to arrive early yesterday, and it paid off. For some reason, they finished Matins 15 minutes ahead of schedule, so in the scramble to make sure everything was ready to go for the Liturgy, I asked if they could use one more, and they took him.
Anyway, Holy Saturday. I don't think most people know what to do with it. Sure, there's Good Friday, when Jesus died on the cross, and of course Easter, when he rose from the dead. But the Gospels don't really spend much time on that day in between. It was the Sabbath, and his disciples rested as they were supposed to. As far as that goes, in one sense we can say that Jesus rested as well. He had completed his work of suffering and dying--really, he had completed his earthly life. By all appearances, he was resting. But we also think of this time as quite active. His soul was in Hades, preaching victory to "the spirits in prison."
In current Orthodox practice, the observance of Holy Saturday actually begins Friday night with the Lamentations service. But even as depressing as that sounds, it contains a great deal of hope in what will soon follow. By the time we get to Holy Saturday itself, the Liturgy is actually attached to Vespers, which really makes it the end of Holy Saturday and the beginning of Easter. So there's a great deal about salvation and victory, which culminates before the Gospel reading, as the altar party processes around the nave and the priest throws bay leaves.