This is my update to the /lib/exits.c and /lib/std/room.c to make obvious exits easier to use and worth with. It adds the following:

• a sub-mapping to the Exits mapping in exits.c to include ([ “obv” : 0 or 1 ]).
• HideExit(dir), which hides the given exit (and should be used in your room code to hide exits)
• GetObvMap(), which returns a mapping of direction and hidden [Example where south is hidden by HideExit(“south”): ([ “west” : 1, “north” : 1, “east” : 1, “south” : 0 ]) ].

Room Exits default to Obvious, so there is no need to set them. The old SetObviousExits and its related functions are still included and valid for compatibility purposes.

I will be releasing another version of this code for use with muds who want more than the [n, s, e, w, u] exit list.

Insert this code into /lib/exits.c:

//Use this to get whether or not an exit is obvious.
int GetExitObv( string str ) {
    if( !Exits[str] ) return 0;
    else return Exits[str]["obv"];
}

//Use this or GetFullExitData to get a mapping of obvious or not, to use for visible/invisible doors in std/room.c
mapping GetObvMap() {
    mapping ret = ([]);
    foreach(string key in keys(Exits)){
	ret[key] = Exits[key]["obv"];
    }

    return ret;
}

//Use this to hide an exit
int HideExit( string dir ) {
	  return Exits[dir]["obv"] = 0;
}

Replace the existing GenerateObviousExits() in /lib/std/room.c with this:

 int GenerateObviousExits(){
    string *normals;
    string *exits;
    string dir_string, enters;
    mapping obv;

    exits = GetExits();
    obv = GetObvMap();

    enters = "";
    normals = ({ "north", "south", "east", "west", "up", "down" });
    normals += ({ "northeast", "southeast", "northwest", "southwest" });
    normals += ({ "out" });
    dir_string = "";

    if(sizeof(GetEnters(1)-({0}))){
			foreach(string enter in this_object()->GetEnters(1)){
			    if (obv["enter "+enter] == 1) {
				    enters += "enter "+enter;
				    if(member_array(enter,this_object()->GetEnters(1)) !=
				     sizeof(this_object()->GetEnters(1)) -1) {
							  enters +=", ";
				    }
			    }
			}
    }

    if(member_array("north",exits) != -1 && obv["north"] == 1) dir_string += "n, ";
    if(member_array("south",exits) != -1 && obv["south"] == 1) dir_string += "s, ";
    if(member_array("east",exits) != -1 && obv["east"] == 1) dir_string += "e, ";
    if(member_array("west",exits) != -1 && obv["west"] == 1) dir_string += "w, ";
    if(member_array("northeast",exits) != -1 && obv["northeast"] == 1) dir_string += "ne, ";
    if(member_array("northwest",exits) != -1 && obv["northwest"] == 1) dir_string += "nw, ";
    if(member_array("southeast",exits) != -1 && obv["southeast"] == 1) dir_string += "se, ";
    if(member_array("southwest",exits) != -1 && obv["southwest"] == 1) dir_string += "sw, ";
    if(member_array("up",exits) != -1 && obv["up"] == 1) dir_string += "u, ";
    if(member_array("down",exits) != -1 && obv["down"] == 1) dir_string += "d, ";
    if(member_array("out",exits) != -1 && obv["out"] == 1) dir_string += "out, ";

    if(sizeof(this_object()->GetEnters(1) - ({0}) )) {
			if(sizeof(this_object()->GetExits())) dir_string += ", ";
			dir_string += enters;
    }

    if(last(dir_string,2) == ", ") dir_string = truncate(dir_string,2);
    dir_string = replace_string(dir_string,", , ",", ");
    if(ObviousVisible) SetObviousExits(dir_string);
    return 1;
}