Ideas wat should go into a users-manual of gtex-letter.

What is it all about. Scoop of the application 
   (personal to business)

Dependencies

Simple letter. More complex ones.
Serial letters

letter headers, multiple letter headers

The different screens, frames.

User interfaces

The rc-file. Configuration

Complex configuration:
 address styles, openings depending on clauses, filename-guesses

LaTeX for non-TeXies
  .tex, .dvi, pdf, ps etc.

Office automation, useful setups

Internationalization. Different TeX-Styles, different Letter-headers