I think everyone here takes it for granted since they've had a Google account since 2005, but I had to setup a couple of accounts recently to utilize G+ and Hangouts and getting friends that weren't part of the network yet was atrocious.
First of all, it looked like I could invite others to my hangout by just an email address, which I did, but they never received the invite. Then we had a hunch that they both had to be part of each others circles, but finding the "Add Friend" functionality where I could simply add an email address was another treasure hunt. FINALLY after finding that dialog buried in the "Circles" dialog, I could add the other account, the other account added me back, and then FINALLY we were able to fire up a Hangout.
Like launching nuclear missels.