Amaya talks about a case where an upstream developer contributed a patch to the Debian package of his software. I'll take this opportunity to mention a couple of positive experiences of my own:
CUPS-PDF is a CUPS backend to generate PDF documents instead of printing out hard copies. Given my complete ignorance of CUPS internals, I figured that I would kindly ask upstream to subscribe himself to the PTS, just in case an RC bug would rear its ugly head.
Volker immediately agreed and, sure enough, someone filed a number of RC bugs resulting from an audit they had performed. Volker replied and argued every point with the submitter by himself, then promptly released a new tarball which included all the fixes.
This is the best case of collaborative maintenance I've encountered so far: Volker maintains his code and I maintain the Debian package. Everybody wins.
Ispell-et is an Estonian wordlist from which all 3 dictionary variants (aspell, ispell, myspell) are generated, plus an hyphenation pattern for OpenOffice, which upstream also uses to generate compound words.
Jaak is a linguistic technology developer whose extremely busy schedule leaves very little time for hobbies. However, the appearance of my package in the Debian repository renewed his interest in maintaining his wordlist. He promptly reviewed my package and suggested a couple of fixes to improve the quality of the dictionary generation process. He also proposed further improvements to eventually generate Hunspell dictionaries as well. Once again, everybody wins.
Wouldn't it be great if all upstream developers subscribed to the Debian PTS for their software and answered bugs related to the codebase themselves?