diff --git a/src/calibre/gui2/__init__.py b/src/calibre/gui2/__init__.py
index 870010b168..bcbb777aca 100644
--- a/src/calibre/gui2/__init__.py
+++ b/src/calibre/gui2/__init__.py
@@ -6,7 +6,7 @@ from threading import RLock
 
 from PyQt4.QtCore import QVariant, QFileInfo, QObject, SIGNAL, QBuffer, Qt, QSize, \
                          QByteArray, QTranslator, QCoreApplication, QThread, \
-                         QEvent, QTimer
+                         QEvent, QTimer, pyqtSignal
 from PyQt4.QtGui import QFileDialog, QMessageBox, QPixmap, QFileIconProvider, \
                         QIcon, QTableView, QApplication, QDialog, QPushButton
 
@@ -236,16 +236,17 @@ def human_readable(size):
     return size + " " + suffix
 
 class Dispatcher(QObject):
-    '''Convenience class to ensure that a function call always happens in the GUI thread'''
-    SIGNAL = SIGNAL('dispatcher(PyQt_PyObject,PyQt_PyObject)')
+    '''Convenience class to ensure that a function call always happens in the
+    thread the reciver was created in.'''
+    dispatch_signal = pyqtSignal(object, object)
 
     def __init__(self, func):
         QObject.__init__(self)
         self.func = func
-        self.connect(self, self.SIGNAL, self.dispatch, Qt.QueuedConnection)
+        self.dispatch_signal.connect(self.dispatch, type=Qt.QueuedConnection)
 
     def __call__(self, *args, **kwargs):
-        self.emit(self.SIGNAL, args, kwargs)
+        self.dispatch_signal.emit(args, kwargs)
 
     def dispatch(self, args, kwargs):
         self.func(*args, **kwargs)
@@ -551,8 +552,9 @@ class Application(QApplication):
 
     def _send_file_open_events(self):
         with self._file_open_lock:
-            self.file_event_hook(self._file_open_paths)
-            self._file_open_paths = []
+            if self._file_open_paths:
+                self.file_event_hook(self._file_open_paths)
+                self._file_open_paths = []
 
 
     def load_translations(self):
@@ -568,7 +570,7 @@ class Application(QApplication):
             if os.access(path, os.R_OK):
                 with self._file_open_lock:
                     self._file_open_paths.append(path)
-                QTimer.singleShot(self._send_file_open_events, 1000)
+                QTimer.singleShot(1000, self._send_file_open_events)
             return True
         else:
             return QApplication.event(self, e)
diff --git a/src/calibre/gui2/ui.py b/src/calibre/gui2/ui.py
index 110224e4f2..756ac113dc 100644
--- a/src/calibre/gui2/ui.py
+++ b/src/calibre/gui2/ui.py
@@ -601,6 +601,8 @@ class Main(MainWindow, Ui_MainWindow, DeviceGUI):
         if dynamic.get('tag_view_visible', False):
             self.status_bar.tag_view_button.toggle()
 
+        self._add_filesystem_book = Dispatcher(self.__add_filesystem_book)
+
 
     def resizeEvent(self, ev):
         MainWindow.resizeEvent(self, ev)
@@ -988,10 +990,11 @@ class Main(MainWindow, Ui_MainWindow, DeviceGUI):
             self.cover_cache.refresh([cid])
             self.library_view.model().current_changed(current_idx, current_idx)
 
-    def _add_filesystem_book(self, paths, allow_device=True):
+    def __add_filesystem_book(self, paths, allow_device=True):
+        print 222, paths
         if isinstance(paths, basestring):
             paths = [paths]
-        books = [os.path.abspath(path) for path in paths is os.access(path,
+        books = [path for path in map(os.path.abspath, paths) if os.access(path,
             os.R_OK)]
 
         if books:
@@ -1003,7 +1006,7 @@ class Main(MainWindow, Ui_MainWindow, DeviceGUI):
 
 
     def add_filesystem_book(self, paths, allow_device=True):
-        Dispatcher(self._add_filesystem_book)(paths, allow_device=allow_device)
+        self._add_filesystem_book(paths, allow_device=allow_device)
 
     def add_books(self, checked):
         '''
@@ -1054,12 +1057,13 @@ class Main(MainWindow, Ui_MainWindow, DeviceGUI):
             self.library_view.model().books_added(self._adder.number_of_books_added)
             if hasattr(self, 'db_images'):
                 self.db_images.reset()
-        if getattr(self._adder, 'critical', None) is not None:
+        if getattr(self._adder, 'critical', None):
             det_msg = []
             for name, log in self._adder.critical.items():
                 if isinstance(name, str):
                     name = name.decode(filesystem_encoding, 'replace')
                 det_msg.append(name+'\n'+log)
+
             warning_dialog(self, _('Failed to read metadata'),
                     _('Failed to read metadata from the following')+':',
                     det_msg='\n\n'.join(det_msg), show=True)