It seems to be expected during a BJ, though sometimes it seems as though it's being done for the sake of it, and can seem a bit fake. There's no substitute for rapport with the WG, eye contact as a part of that is great, but without the rapport, eye contact on its own can be unnerving and distracting.
From a girl with a great set of lanterns it can be spectacular. Delilah Dash has been discussed on here recently, and I remember having her blue eyes looking up at me was something else.