diff --git a/shell/PresenceWindow.py b/shell/PresenceWindow.py
index c9ec5585..16544a5c 100644
--- a/shell/PresenceWindow.py
+++ b/shell/PresenceWindow.py
@@ -40,6 +40,12 @@ class PresenceWindow(gtk.Window):
 	def set_activity(self, activity):
 		self._activity = activity
 		self._update_buddies_visibility()
+		if activity:
+			if self._activity.get_shared():
+				self._share_button.set_sensitive(False)
+			else:
+				self._share_button.set_sensitive(True)
+			self._activity.connect('shared', lambda w: self._share_button.set_sensitive(False))
 
 	def _setup_ui(self):
 		vbox = gtk.VBox(False, 6)
@@ -87,10 +93,10 @@ class PresenceWindow(gtk.Window):
 
 		button_box = gtk.HButtonBox()
 
-		share_button = gtk.Button('Share')
-		share_button.connect('clicked', self._share_button_clicked_cb)
-		button_box.pack_start(share_button)
-		share_button.show()
+		self._share_button = gtk.Button('Share')
+		self._share_button.connect('clicked', self._share_button_clicked_cb)
+		button_box.pack_start(self._share_button)
+		self._share_button.show()
 
 		vbox.pack_start(button_box, False)
 		button_box.show()
diff --git a/shell/shell.py b/shell/shell.py
index 87db70f2..895d3c12 100755
--- a/shell/shell.py
+++ b/shell/shell.py
@@ -19,11 +19,25 @@ from StartPage import StartPage
 from WindowManager import WindowManager
 from PresenceWindow import PresenceWindow
 
-class ActivityHost(dbus.service.Object):
+class ActivityHostSignalHelper(gobject.GObject):
+	__gsignals__ = {
+		'shared': (gobject.SIGNAL_RUN_FIRST, gobject.TYPE_NONE, ([]))
+	}
 
+	def __init__(self, parent):
+		gobject.GObject.__init__(self)
+		self._parent = parent
+
+	def emit_shared(self):
+		self.emit('shared')
+
+class ActivityHost(dbus.service.Object):
 	def __init__(self, activity_container, activity_name, default_type, activity_id = None):
 		self.activity_name = activity_name
 		self.ellipsize_tab = False
+		self._shared = False
+
+		self._signal_helper = ActivityHostSignalHelper(self)
 
 		self.activity_container = activity_container
 		
@@ -113,6 +127,18 @@ class ActivityHost(dbus.service.Object):
 		#print "window_id = %d"%window_id
 		return window_id
 
+	def connect(self, signal, func):
+		self._signal_helper.connect(signal, func)
+
+	def get_shared(self):
+		"""Return True if this activity is shared, False if
+		it has not been shared yet."""
+		return self._shared
+
+	def _shared_signal(self):
+		self._shared = True
+		self._signal_helper.emit_shared()
+
 	@dbus.service.method("com.redhat.Sugar.Shell.ActivityHost", \
 			 in_signature="ss", \
 			 out_signature="")
@@ -123,6 +149,11 @@ class ActivityHost(dbus.service.Object):
 		self.peer_service = dbus.Interface(self.activity_container.bus.get_object( \
 				self.__peer_service_name, self.__peer_object_name), \
 										   "com.redhat.Sugar.Activity")
+		self.activity_container.bus.add_signal_receiver(self._shared_signal,
+				signal_name="ActivityShared",
+				dbus_interface="com.redhat.Sugar.Activity",
+				named_service=self.__peer_service_name,
+				path=self.__peer_object_name)
 
 	@dbus.service.method("com.redhat.Sugar.Shell.ActivityHost", \
 			 in_signature="b", \
@@ -213,6 +244,11 @@ class ActivityHost(dbus.service.Object):
 		get_id() function."""
 		return self.activity_id
 
+	def default_type(self):
+		"""Interface-type function to match activity.Activity's
+		default_type() function."""
+		return self._default_type
+
 	def get_object_path(self):
 		return self.dbus_object_name
 
diff --git a/sugar/activity/Activity.py b/sugar/activity/Activity.py
index 2af336a2..1cf9f946 100644
--- a/sugar/activity/Activity.py
+++ b/sugar/activity/Activity.py
@@ -141,6 +141,11 @@ class ActivityDbusService(dbus.service.Object):
 		"""Called by the shell to request the activity to publish itself on the network."""
 		self._call_callback(ON_PUBLISH_CB)
 
+    @dbus.service.signal(ACTIVITY_SERVICE_NAME)
+	def ActivityShared(self):
+		print "sent signal"
+		pass
+
 class Activity(object):
 	"""Base Activity class that all other Activities derive from."""
 
@@ -157,6 +162,7 @@ class Activity(object):
 		self._plug = None
 		self._initial_service = None
 		self._activity_object = None
+		self._shared = False
 		if type(default_type) != type("") or not len(default_type):
 			raise ValueError("Default type must be a valid string.")
 		self._default_type = default_type
@@ -180,6 +186,15 @@ class Activity(object):
 	def default_type(self):
 		return self._default_type
 
+	def set_shared(self):
+		"""Mark the activity as 'shared'."""
+		if not self._shared:
+			self._shared = True
+			self._dbus_service.ActivityShared()
+
+	def shared(self):
+		return self._shared
+
 	def has_focus(self):
 		"""Return whether or not this Activity is visible to the user."""
 		return self._has_focus
@@ -197,6 +212,8 @@ class Activity(object):
 		print "Activity: XEMBED window ID is %s" % self._window_id
 		self._plug = gtk.Plug(self._window_id)
 		self._initial_service = service
+		if service:
+			self.set_shared(True)
 		self.on_connected_to_shell()
 
 	def _internal_on_disconnected_from_shell_cb(self):
diff --git a/sugar/presence/PresenceService.py b/sugar/presence/PresenceService.py
index c379b856..95990259 100644
--- a/sugar/presence/PresenceService.py
+++ b/sugar/presence/PresenceService.py
@@ -492,6 +492,10 @@ class PresenceService(gobject.GObject):
 			# random port #
 			port = random.randint(5000, 65535)
 
+		# Mark the activity as shared
+		if stype == activity.default_type():
+			activity.set_shared()
+
 		logging.debug('Share activity %s, type %s, address %s, port %d, properties %s' % (actid, stype, address, port, properties))
 		service = Service.Service(name=real_name, stype=stype, domain="local",
 				address=address, port=port, properties=properties)