Let me point out two recent literate programming successes -

1. darcs. The (haskell) code and (latex) manual are intermingled and 
maintained as a single unit to very good effect. See the manual at 
http://darcs.net .

2. ruby. http://www.ruby-doc.org/core and http://www.ruby-doc.org/stdlib 
present current, accessible API docs and also higher level docs with very 
little fuss. These are generated from extensive code comments, READMEs, 
etc. (Many other languages do this but less effectively.)

Cheers,
-Simon

PS I really like this thread.