Doubt this would be of interest to many people I know, because it's really more relevant to older fandom content that was on there, but it looks like yahoo groups is shutting down on October 21st! :(
I think the yahoo group I’d most miss would be fanfic_med. I was still hoping to be able to search the archives of that for whump advice. Dunno if there’s gonna be any plans to archive any of the groups anywhere else.
I also remember having a good time over on the SGAHC yahoo group, where they put up politely with my inexperienced fannish arse not knowing certain fannish etiquette at first, especially about posting fics. I’ll have to see about saving anything interesting from my two groups - I ran weirmckayship and weirmckaysmut over there although those mostly went inactive once we had the mcweir.com fansite I used to run.