Nice work Geoff.

The code looks good, just marking as "Needs fixing" as there are some aesthetics that could be worked out.

[1]

82	+    def __init__(self, configuration):
83	+        self.__lock_out = True
84	+        self.__lock = threading.Lock()
85	+        self.__initial_server_host_name = self.DEFAULT_SERVER_HOST_NAME
86	+        self.__configuration = configuration
87	+        self.__configuration
88	+        self.__configuration.load([])
89	+        self.__load_data_from_config()
90	+        self.__modified = False
91	+        self.unlock()

We don't need that self.__configuration in 87.


[2]

93	+    def default_dedicated(self):
94	+        """
95	+        Set L{server_host_name} to something sane when switching from hosted to
96	+        dedicated
97	+        """

We need a period at the end of line.


[3]

160	+    def __derive_server_host_name_from_url(self, url):
161	+        "Extract the hostname part from a url"
162	+        try:
163	+            without_protocol = url[url.index("://") + 3:]
164	+        except ValueError:
165	+            without_protocol = url
166	+        try:
167	+            return without_protocol[:without_protocol.index("/")]
168	+        except ValueError:
169	+            return without_protocol

Maybe we could store the result of urlparse.urlparse(url) and reuse it whenever we need it.
Also, the docstring must be a sentence ending with a period. I've observed it in some other methods as well.

[4]

354	+    def setUp(self):
355	+        super(LandscapeSettingsApplicationControllerUISetupTest, self).setUp()
356	+
357	+        def fake_run(obj):
358	+            """
359	+            Retard X11 mapping.
360	+            """
361	+            pass
362	+        self._real_run = Gtk.Dialog.run
363	+        Gtk.Dialog.run = fake_run

Do you think the test suite will evolve much more for GUI? Maybe we could have another iteration to create some GUI specific base class and add stuff like this in it.

[5]

365	+        def get_config():
366	+            configdata = """
367	+[client]
368	+data_path = %s
369	+http_proxy = http://proxy.localdomain:3192
370	+tags = a_tag
371	+url = https://landscape.canonical.com/message-system
372	+account_name = foo
373	+registration_password = bar
374	+computer_title = baz
375	+https_proxy = https://proxy.localdomain:6192
376	+ping_url = http://landscape.canonical.com/ping
377	+
378	+""" % sys.path[0]

Maybe we could make it less unindented:

    def get_config():
        configdata = ("[client]"
                     "data_path = %s"
                     "http_proxy = http://proxy.localdomain:3192"
                      "tags = a_tag"
                      "url = https://landscape.canonical.com/message-system"
                      "account_name = foo"
                      "registration_password = bar"
                      "computer_title = baz"
                      "https_proxy = https://proxy.localdomain:6192"
                      "ping_url = http://landscape.canonical.com/ping") % sys.path[0]

[6]

381	+            class MyLandscapeSettingsConfiguration(
382	+                LandscapeSettingsConfiguration):
383	+                default_config_filenames = [config_filename]
384	+            config = MyLandscapeSettingsConfiguration(None)
385	+            return config
386	+        self.app = ConnectionRecordingLandscapeSettingsApplicationController(
387	+            get_config_f=get_config)

Maybe we could make it a little easier on the eyes:

381	+            class MyLandscapeSettingsConfiguration(
382	+                LandscapeSettingsConfiguration):
383	+                default_config_filenames = [config_filename]
384	+
385	+
386	+            config = MyLandscapeSettingsConfiguration(None)
387	+            return config
388	+
389	+        self.app = ConnectionRecordingLandscapeSettingsApplicationController(
390	+            get_config_f=get_config)

[7]

418	+    def setUp(self):
419	+        super(ConfigControllerTest, self).setUp()
420	+        config = """
421	+[client]
422	+data_path = /var/lib/landscape/client
423	+http_proxy = http://proxy.localdomain:3192
424	+tags = a_tag
425	+url = https://landscape.canonical.com/message-system
426	+account_name = foo
427	+registration_password = bar
428	+computer_title = baz
429	+https_proxy = https://proxy.localdomain:6192
430	+ping_url = http://landscape.canonical.com/ping
431	+
432	+"""

If you consider the indentation I proposed up there, maybe you could fix this one as well.

And the same goes for:

435	+        class MyLandscapeSettingsConfiguration(LandscapeSettingsConfiguration):
436	+            default_config_filenames = [self.config_filename]
437	+        self.config = MyLandscapeSettingsConfiguration(None)

Also in this block:

938	+    def setUp(self):
939	+        super(ConfigurationViewCommitTest, self).setUp()
940	+        config = """
941	+[client]
942	+data_path = %s
943	+http_proxy = http://proxy.localdomain:3192
944	+tags = a_tag
945	+url = https://landscape.canonical.com/message-system
946	+account_name = foo
947	+registration_password = bar
948	+computer_title = baz
949	+https_proxy = https://proxy.localdomain:6192
950	+ping_url = http://landscape.canonical.com/ping
951	+""" % sys.path[0]
952	+        self.config_filename = self.makeFile(config)
953	+
954	+        class MyLandscapeSetupConfiguration(LandscapeSetupConfiguration):
955	+            default_config_filenames = [self.config_filename]
956	+        self.config = MyLandscapeSetupConfiguration(None)
957	+        self.real_write_back = LandscapeClientSettingsDialog._write_back
958	+        self.write_back_called = False

Line breaks in between 955 and 956.

959	+
960	+        def fake_write_back(obj):
961	+            self.write_back_called = True
962	+        LandscapeClientSettingsDialog._write_back = fake_write_back
963	+        self.controller = ConfigController(self.config)
964	+        self.dialog = LandscapeClientSettingsDialog(self.controller)

Like breaks between 961 and 962.

You can double check all the setUp code in the tests as you define the config every time and check that we have the same pattern.

Thanks!