Do not add books to the list of books on device if they are already in the list. Fixes book showing up multiple times if it it sent to the device multiple times. Only one istance of the book will be on the device in this case.

src/calibre/devices/usbms/books.py

@@ -18,6 +18,9 @@ def __init__(self, path, title, authors, mime):
         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'''

src/calibre/devices/usbms/driver.py

@@ -109,7 +109,7 @@ def get_size(obj):
             if not os.path.exists(newpath):
                 os.makedirs(newpath)
             
-            filepath = os.path.join(newpath, names.next())                
+            filepath = os.path.join(newpath, names.next())
             paths.append(filepath)
             
             if hasattr(infile, 'read'):
@@ -132,7 +132,10 @@ def add_books_to_metadata(cls, locations, metadata, booklists):
             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: