If I may inject an opinion on congrats and thanks, I don't see how public congrats and thanks are better than private congrats and thanks. Public congrats makes sense if the one congratulated was too shy to mention his accomplishment himself onlist, but otherwise congrats can come off as the congratulator trying to score appearance points.
Likewise public thanks make sense if the thanker has no other means of communicating with the congratulator, but otherwise it can be done just as well offlist.
The way I see it—more opinion—if one were really sincere in wanting to congratulate another, the congratulator wouldn't mind the "trouble" of a private message. Onlist congrats can have the feeling of piggybacking and can be pretty hollow, and a cookie-cutter congratulations most often elicits a cookie-cutter thanks.
As a congratulator, when searching the list for publication announcements also check whether an announcement has already received congrats. If so, please send your congrats privately.