Well, being a den leader my group is small. But I set up a shutterfly share site.
It allows us to share all the photos we take with each other. (this was the initial reason I wanted the site)
I can set up my den roster with all the parent contact info.
It has a calender on which I can set events.
I can set up events to automatically send a reminder e-mail to all the parents on the roster.
If I make a change to an event on the calender it asks if I would like to send a change notice e-mail.
I can set up additional members that do not automatically get reminders, but can be added to e-mails.
I can post documents for the parents, like PDF files of forms or PWD rules.
On the front page I have a feed from the council website of upcoming council activites.
Only members can access the site.
I can set up multiple "owners" who can modify the site.
Minuses based on my needs:
I can't attach documents to e-mails.
It's another calender to maintain.
No advancement tracking.