Mingw32 mailing list is kind to host PW32 discussions. While it's possible to create own mailing list with SourceForge, I dislike separatism tendencies. Mingw32 list is enough lived-in now, so there's chances to get help or at least directions there.
Before you report bug, make sure that you have what to report. Simple statements like "it doesn't" doesn't work. If you never thought what it is - to report bug, take a minute to read wonderful Simon Tatham's essay "How to Report Bugs Effectively".
The best way to report bugs is via bug tracking system. This will allow to have organized bug-resolving cycle for developers and proper feedback for users. Please note that you should post bugreports while being logged in with your SourceForge name, if you want to stay current with bug's lifecycle (you will be recieving e-mail notifications whenever bug status changes).
For the people interested in implementation issues of PW32 on in developing it, special mailing list is set up:
Mailing lists below also may be of interest. But note that they are note appropriate place for discussing PW32, but rather for general POSIX/Unix questions on Windows.