<<Casey, my 6 yr old rough
collie, rarely barks.  When she does, I take it very seriously.  And if
she growls, it is time to call 911.>>

My collies will bark some when they play, but only lasts a minute or two.
 Otherwise, they are just like you describe Casey.  Of course, with our
predator level out here, they often bark more at night, but like you said,
if they are barking, we know there is something threatening out there and
if they are barking and growling it is time to get out the shotgun!

The last two collies we had was years ago when we lived in a more suburban
location.  They never barked at all (no coyotes to warn off!).  The only
time I ever remember our male collie barking at night was once when the
police broke down the outside door into the bathroom in the middle of the
night because somebody had called 911 about a prowler outside our house.
 Even then he didn't really bark but just gave a muffled "woof" as he raced
past our bed toward the bathroom.  Fortunately for the policeman, my
husband was right behind the dog heading for whoever was breaking in and
called him off.  It was a total surprise to the police to see this huge dog
bearing down on them when they hadn't even heard him bark.

Sandra