Great Article on Design Prototyping

Creating Passionate Users: Don't make the Demo look Done

When we show a work-in-progress (like an alpha release) to the public, press, a client, or boss... we're setting their expectations. And we can do it one of three ways: dazzle them with a polished mock-up, show them something that matches the reality of the project status, or stress them out by showing almost nothing and asking them to take it 'on faith' that you're on track.

The bottom line:
How 'done' something looks should match how 'done' something is.