When we first started using online tutorials (Elluminate), advice was to avoid the use of webcams because the quality was not good enough.  However, I recently saw an OU document recommending the use of webcams by the tutor and I have been switching it on recently.  Student response seems to be quite favourable with comments like "It is good to put a face to the name and voice", which slightly surprised me as most of the time I focus on the whiteboard, slides and chat.  However, if it makes a difference to how students feel about the experience, I am very happy to have my webcam on.