I have 3 Yahoo groups...
One is 4.5 years old and is called "Hardcore India" which has over 3000 members. I started one for Sahara last Aug/Sep which now has over 1000. These both have posts made now and again but are really handy for me to spam my various sites to surfers legally
I never touch my third group and this still has over 600 members and I only post there to promote my sites once every few months.
Most members of Yahoo groups are free loaders and only want to see the sample images I add to folders rather than pay to join the sites my groups promote but... there are the odd one or two I'm sure who do eventually pay out some cash
I also have my groups fully moderated to keep out other spammers. I have a few surfers who try to post a few pics with an invitation to join their group. I edit out their invitation and just allow the pics... LOL.
I started a Google group last year and it's done zilch... So stick to Yahoo is my advise