...

src/calibre/ebooks/metadata/sources/base.py

@@ -181,6 +181,10 @@ class Source(Plugin):
     #: construct the configuration widget for this plugin
     options = ()
 
+    #: A string that is displayed at the top of the config widget for this
+    #: plugin
+    config_help_message = None
+
 
     def __init__(self, *args, **kwargs):
         Plugin.__init__(self, *args, **kwargs)

src/calibre/ebooks/metadata/sources/isbndb.py

@@ -39,6 +39,12 @@ class ISBNDB(Source):
                     'at isbndb.com and get an access key.')),
             )
 
+    config_help_message = '<p>'+_('To use metadata from isbndb.com you must sign'
+            ' up for a free account and get an isbndb key and enter it below.'
+            ' Instructions to get the key are '
+            '<a href="http://isbndb.com/docs/api/30-keys.html">here</a>.')
+
+
     def __init__(self, *args, **kwargs):
         Source.__init__(self, *args, **kwargs)
 

src/calibre/gui2/metadata/config.py

@@ -56,7 +56,12 @@ class ConfigWidget(QWidget):
         self.setLayout(l)
 
         self.gb = QGroupBox(_('Downloaded metadata fields'), self)
-        l.addWidget(self.gb, 0, 0, 1, 2)
+        if plugin.config_help_message:
+            self.pchm = QLabel(plugin.config_help_message)
+            self.pchm.setWordWrap(True)
+            self.pchm.setOpenExternalLinks(True)
+            l.addWidget(self.pchm, 0, 0, 1, 2)
+        l.addWidget(self.gb, l.rowCount(), 0, 1, 2)
         self.gb.l = QGridLayout()
         self.gb.setLayout(self.gb.l)
         self.fields_view = v = QListView(self)
@@ -81,7 +86,7 @@ class ConfigWidget(QWidget):
             widget.setValue(val)
         elif opt.type == 'string':
             widget = QLineEdit(self)
-            widget.setText(val)
+            widget.setText(val if val else '')
         elif opt.type == 'bool':
             widget = QCheckBox(opt.label, self)
             widget.setChecked(bool(val))

src/calibre/gui2/preferences/metadata_sources.py

@@ -10,7 +10,7 @@ __docformat__ = 'restructuredtext en'
 from operator import attrgetter
 
 from PyQt4.Qt import (QAbstractTableModel, Qt, QAbstractListModel, QWidget,
-        pyqtSignal, QVBoxLayout, QDialogButtonBox, QFrame, QLabel)
+        pyqtSignal, QVBoxLayout, QDialogButtonBox, QFrame, QLabel, QIcon)
 
 from calibre.gui2.preferences import ConfigWidgetBase, test_widget
 from calibre.gui2.preferences.metadata_sources_ui import Ui_Form
@@ -67,6 +67,13 @@ class SourcesModel(QAbstractTableModel): # {{{
             return self.enabled_overrides.get(plugin, orig)
         elif role == Qt.UserRole:
             return plugin
+        elif (role == Qt.DecorationRole and col == 0 and not
+                    plugin.is_configured()):
+            return QIcon(I('list_remove.png'))
+        elif role == Qt.ToolTipRole:
+            if plugin.is_configured():
+                return _('This source is configured and ready to go')
+            return _('This source needs configuration')
         return NONE
 
     def setData(self, index, val, role):

src/calibre/gui2/preferences/metadata_sources.ui

@@ -48,6 +48,16 @@
             </property>
            </widget>
           </item>
+          <item>
+           <widget class="QLabel" name="label_5">
+            <property name="text">
+             <string>Sources with a red X next to their names must be configured before they will be used. </string>
+            </property>
+            <property name="wordWrap">
+             <bool>true</bool>
+            </property>
+           </widget>
+          </item>
           <item>
            <widget class="QPushButton" name="configure_plugin_button">
             <property name="text">