Ok, now that I've read this whole thread, here are my thought on the description. I think the dialogue is one of those items that should be self-explanatory via the descriptions so whether you use O.S. or not, you should do it consistently.

For descriptions, I am of the persuasion of write what can be shown (or heard) on screen. If an invisible man were in a bed, you would see an indention in the bed, not the man. If this man got out of bed, you would note the indention goes away and you might hear a grunt. Everything this character does would be know only via his voice or via his interaction with visible objects so the description would only involve what is actually shown on screen.

Our job is to tell what the audience will see on screen, and nothing more. To tell what an invisible man is doing is like saying that a visible person is feeling sad. You have to tell this visually so when the invisible man walks across the room, you see footprints appears. When he walks out a door, you see the door open and close. Likewise, when a person is sad, you see a tear drop down their cheek and perhaps they sniffle.

It's all about the visual. If you can't see it, leave it out.