I've found that it's often worth unit-testing functionality that depends upon complex combinations of GUI state. For example, "Show the menu only when there is a selected bar and the baz list contains at least two items that can be foozled together." These interactions are very often wrong, and even if you code them right, it's nice to have a record of what the spec was so when someone comes along and says "I can make this code much cleaner if I eliminate the check for foozling" (or worse, they change the definition of foozling), the test breaks and you remember there was a reason you put it there in the first place.

I find that it's a waste to test things like appearance, position, labels - basically anything that should be in CSS or other declarative specifications. But UIs often have quite a bit of actual logic in them (ironically, because real humans are often strikingly illogical), and that should all get tested.