There’s a great discussion about eye contact in photojournalism on the NYT photo blog, LENS. The discussion (which is more interesting than the photos themselves, imo) applies to anyone, like myself, who shoots street photos.
The issues, however, are not unique to street photography and photojournalism. They are the same issues that one encounters in nude photography and portraiture in general. Eye contact with the subject makes an image a 3 way disclosure in that the subject of the photo is both collusive and self-composing, as though the photographer is showing the viewer to the subject for unknown or assumed reasons. Minus the eye contact, a photo is more like a thought offered for sharing by the photographer with the viewer.