WatiN best practices/rules of thumb for an ASP.NET MVC app -

I am a fond TDD and a BDD fan but have not done a lot in UI test methods. I have an ASP.NET MVC3 application with several MSPEC tests and I want to add presentation test using WatiN.

What kind of things do you check? Do I have to write a test for the initial weight of the UI or for things that have been changed due to user interaction only?

While writing WatiN (and UI), what are the best rules and best practices in thumb? I test in general)

Where I work now, we test these 5 things (where applicable) each page:

1. Layout - Text labeled in x Box, dropdown label should be
2. Populate - should have dropdown with the values ​​given below ... in textbox
3. Validate - When I enter X, then I should navigate the error message Y
4. - When I click on the X button, then go to the Y page
5. Save - When I click the Save button, I should see the success message