I set up git-annex on my mom's and sisters' computers a couple of months ago. I noticed this was the first software I've written that I didn't have to really explain how to use. All I told them was, put files in this folder, and the rest of us will be able to see them. Don't put anything too big in there, or anything you don't want others to see.
I paired the computers using XMPP, and set up an encrypted transfer repository using a free account rsync.net gave me for beta testing. I also added a repository on my server, which made things more robust. (XMPP has since improved, but it's still a good idea to have a git repository to suppliment XMPP.) I also have two removable drives that are used to back up our files.
This was all set up using the webapp. And adding a computer takes just a couple of minutes that way. I set it up at my sister's in a spare moment during a visit, and it all just worked.
Our shared git annex contains a couple of hundred files, and is a couple of gigabytes in size. And growing pretty fast as we find things we want to share. Mostly photos and videos so far but I won't be surprised to find poems and books pop up in there from the family's poets and authors. And it'll grow further as I add people who've so far been left out.
Coming home from a week at the beach with my grand nephew and niece, was the first time I really used git-annex without thinking about it. Collapsed on a hotel bed, I plugged in my camera and loaded in the trip's photos. Only to see the hotel wifi cost extra. Urk, no! Later, in the lobby, I found an open wifi network, and watched it automatically sync up.
By the time I was home, the video of cute kids playing weathermen and reporting on our near miss by a tropical storm had been enjoyed by the folks who didn't make that family gathering.