I'm a big fan of this request. Developer IDEs have the concept of a "Closed" Project which removes its reference from search and other places. Projects (in the case of Evernote, Notebooks or Stacks) can be easily closed or reopened.
My specific use case is that I have notes and materials from past projects and companies that I want to ignore in my current working context. I have similar notebook naming patterns for different areas of my work and responsibilities and it slows me down to have to select "the right" notebook from the new project.
