I guess it depends on what you use in there - thinking about it I've only ever used the same image in there that I've used in other places in the same texture, and I don't think they worked too well, cos I'd click in the same channel that say diffuse was using, and usually that made the resultant material very dark.

I've just tested it using one of my sky photos, and even that can darken the texture too much.  There must be a trick to using it.

Measure your mind's height
by the shade it casts.
Robert Browning (Paracelsus)

Fran's Freestuff

http://franontheedge.blogspot.com/

http://www.FranOnTheEdge.com