Hmm, I'm not sure about that one, does anyone know of any studies or have any opinions related to darkening the sides?
Widescreen movies on a 4:3 aspect TV always use black edges, but maybe that's just tradition or to do with contrast or something like that.
EDIT: Just noticed that HN has a grey content area with white around the edges, which I like, so maybe my preference is more to do with having different colour sides than dark sides - i.e. some kind of boundary to the content area.