A lot of space is given to eye contact, but I am not all that keen to rely on it because it is not always possible. Maybe it's because I am also a singer, and often I am facing the audience with my mouth to the microphone and I don't have the luxury of looking behind me while I'm also trying to sing and play the bass to guess at what someone else might be doing.
I will look at the bandleader who I like to have to my right because I can look across at him without moving away from the mic, and I can look at the drummer when songs are ending if I'm not singing all the way to the end. But to suggest strong reliance on those sorts of cues is sort of saying "don't bother to learn how it goes," and I think that does the music a disservice. Even in the bands that are primarily improvisational, there's a certain amount of understanding about what's at least coming next, and if I have cues that I can hear, that's more reliable for me that cues I have to visualize. Not every stage setup lends itself easily to line of sight, either.
But, like many things, I've softened my view on this somewhat over the past five years, because people tend to want to do these things and in some cases nobody's had time to learn the material well enough to do it in any better way. I just wouldn't suggest it as a preferred method or something to choose over actually learning the songs and developing arrangement points, in most cases.
