I've blogged about text based GUI mockups before. I think they're useful.

Here's one I did today, it took about one minute. It was to clarify how a use case would work.

I wrote it as part of an email in Outlook, using the Courier font. I also used the foreground/background colouring in Outlook to make it stand out from the rest of the email.

A bit silly, but possibly effective :) 1980's eat your heart out...