diff --git a/src/calibre/devices/cybookg3/driver.py b/src/calibre/devices/cybookg3/driver.py
index 495a7f1b81..f05b28b538 100644
--- a/src/calibre/devices/cybookg3/driver.py
+++ b/src/calibre/devices/cybookg3/driver.py
@@ -52,10 +52,10 @@ class CYBOOKG3(USBMS):
                 return size
             return os.path.getsize(obj)
 
-        sizes = map(get_size, files)
+        sizes = [get_size(f) for f in files]
         size = sum(sizes)
 
-        if on_card and size > self.free_space()[2] - 1024*1024: 
+        if on_card and size > self.free_space()[2] - 1024*1024:
             raise FreeSpaceError(_("There is insufficient free space on the storage card"))
         if not on_card and size > self.free_space()[0] - 2*1024*1024: 
             raise FreeSpaceError(_("There is insufficient free space in main memory"))
diff --git a/src/calibre/devices/usbms/books.py b/src/calibre/devices/usbms/books.py
index 3943ef94f4..fffed41549 100644
--- a/src/calibre/devices/usbms/books.py
+++ b/src/calibre/devices/usbms/books.py
@@ -18,6 +18,9 @@ class Book(object):
         self.thumbnail = None
         self.tags = []
         
+    def __eq__(self, other):
+        return self.path == other.path
+        
     @apply
     def title_sorter():
         doc = '''String to sort the title. If absent, title is returned'''
diff --git a/src/calibre/devices/usbms/device.py b/src/calibre/devices/usbms/device.py
index 1d3aba37de..dcab2d7936 100644
--- a/src/calibre/devices/usbms/device.py
+++ b/src/calibre/devices/usbms/device.py
@@ -191,7 +191,6 @@ class Device(_Device):
         self._main_prefix = drives.get('main', None)
         self._card_prefix = drives.get('card', None)
 
-    @classmethod
     def get_osx_mountpoints(self, raw=None):
         if raw is None:
             ioreg = '/usr/sbin/ioreg'
@@ -227,11 +226,11 @@ class Device(_Device):
         dev_pat = r'/dev/%s(\w*)\s+on\s+([^\(]+)\s+'
         if 'main' not in names.keys():
             raise DeviceError(_('Unable to detect the %s disk drive. Try rebooting.')%self.__class__.__name__)
-        main_pat = dev_pat%names['main']
+        main_pat = dev_pat % names['main']
         self._main_prefix = re.search(main_pat, mount).group(2) + os.sep
         card_pat = names['card'] if 'card' in names.keys() else None
         if card_pat is not None:
-            card_pat = dev_pat%card_pat
+            card_pat = dev_pat % card_pat
             self._card_prefix = re.search(card_pat, mount).group(2) + os.sep
 
     def open_linux(self):
diff --git a/src/calibre/devices/usbms/driver.py b/src/calibre/devices/usbms/driver.py
index 10e655ac39..482ddedbb8 100644
--- a/src/calibre/devices/usbms/driver.py
+++ b/src/calibre/devices/usbms/driver.py
@@ -34,7 +34,8 @@ class USBMS(Device):
     SUPPORTS_SUB_DIRS = False
 
     def __init__(self, key='-1', log_packets=False, report_progress=None):
-        pass
+        Device.__init__(self, key=key, log_packets=log_packets, 
+                        report_progress=report_progress)
 
     def get_device_information(self, end_session=True):
         """
@@ -54,7 +55,8 @@ class USBMS(Device):
 
         # Get all books in all directories under the root ebook_dir directory
         for path, dirs, files in os.walk(os.path.join(prefix, ebook_dir)):
-            # Filter out anything that isn't in the list of supported ebook types
+            # Filter out anything that isn't in the list of supported ebook
+            # types
             for book_type in self.FORMATS:
                 for filename in fnmatch.filter(files, '*.%s' % (book_type)):
                     title, author, mime = self.__class__.extract_book_metadata_by_filename(filename)
@@ -80,7 +82,7 @@ class USBMS(Device):
                 return size
             return os.path.getsize(obj)
 
-        sizes = map(get_size, files)
+        sizes = [get_size(f) for f in files]
         size = sum(sizes)
 
         if on_card and size > self.free_space()[2] - 1024*1024:
@@ -131,7 +133,11 @@ class USBMS(Device):
             on_card = 1 if location[1] else 0
 
             title, author, mime = cls.extract_book_metadata_by_filename(os.path.basename(path))
-            booklists[on_card].append(Book(path, title, author, mime))
+            book = Book(path, title, author, mime)
+
+            if not book in booklists[on_card]:
+                booklists[on_card].append(book)
+
 
     def delete_books(self, paths, end_session=True):
         for path in paths: