QUOTE (Simon @ Feb 17 2006, 12:20 PM)

Do most companies assure the understudy of at least one performance? I have experienced one person saying they didn't want to put in all the effort of learning a part to understudy if they would only get to perform the role in case of emergency, which seems to happen quite infrequently. I can understand that feeling (even if it isn't very "team-minded"), but on the other hand, if a run only consists of, say, 4 performances, to take one away from the the appointed lead seems a bit much.
My general run is 3 performances, so I have encountered the same issue. You need to be prepared in case the unfortunate should happen, but you don't want to waste your time rehearsing when someone won't perform the part.
I generally have my leads understudied by my supporting actors, and my supporting actors understudied by my bit parts. I have my stage manager or myself understudy the bit part. If an actor misses a rehearsal, I move the understudies into the new positions. I require my understudies to keep the blocking for the other characters as well as attend all rehearsals. As I have a problem with actors talking in the background during rehearsal [see Things that annoy directors thread], I use my understudies as a weapon in shaping up the disobedient.
Since they have the honor and privilege of being the understudy, my actors have to be ready to step into the role at a moment's notice. I also try to leave some time available in tech week in case I have to rehearse an understudy at the last minute. If nothing else, I'll take over a tech rehearsal and send my stage manager out in the lobby to rehearse the replacement actor.
I expect my actors to be up on their blocking and characterization. I expect them to talk to the actors they are understudying about characterization and background info. However, I do not guarantee performances in those roles. It's just not fair to the person who was assigned the role in the first place. I also don't do "double casting" and have half the cast in one role one night and swap to another the next night.
One of my colleagues did actually swap out actors for 1 performance of a 3-performance run, and it worked against them. This director didn't have enough time to rehearse both casts, so neither performance was stunning.
I hope this answers your questions.