With a good design pattern like MVP, MVC, etc we aim to move all logic out of the GUI. That leaves us with a light weight GUI which ideally just need to "bind" its buttons and fields to properties in some business logic layer. This is a great approach as this layer will be free from GUI stuff, and we can easily write unit tests for it.
My question is: Is this enough? Or should we still unit test the GUI layer?
IMHO if you remove whole logic from GUI, you don't need to test it automatically. Of course you still need to run it to see if it looks like it should :)
This is about unit tests. For integration tests it is still good to test everything, e.g. by Selenium, if possible.
Sometime the GUI is not really that dumb. For instance there might be drag and drop support, custom components which display their content based on where they are placed and many more. In that case these things need to be specifically tested both in integration tests and individually in unit tests.
Most of the time the integration tests start from the UI layer and we end up testing a lot of UI layer in those scenarios as well. I once read a comment from someone about unit-testing that you don't need to write tests for code that can be easily broken for instance getters/setters can be easily broken (for example getter returns the value it is supposed to do and we can break it easily by not returning the value) so we don't end up writing unit tests for getter and setters unless there is some logic embedded in it (in which case these are not actually getter and setters).
So if the GUI is totally dumb and there is only bindings in it then unit tests are not required.