I used to work at a major charity for the blind. Yes the dogs were incredible - their handlers more so.
One good friend of mine was severely visually impaired and had a dog with the worst flatulence ever. used to stink the whole office out. However, on the really funny side, my friend was attacked on a London tube platform by two try it on muggers. Dog did naff all, my friend on the other hand who had achieved extremely high levels in one particular martial art gave these two a fair kicking. Served them right.