If you are building apps for people other than yourself, then having a banner to notify them it won't work is better than a blank page.

A typical banner that I make includes the following things:

- Positioned at the top via CSS and sticks there

- Includes a link to http://www.enable-javascript.com

- Includes a tracking image so I can see how many people are coming without JS enabled

If you have a white page like this blog does, people will think your site is broken and bounce... and may never come back.