There doesn't seem to be a way of involving small groups of people in small discussions that don't require a lot of attention. Someone else mentioned D&D groups -- that's exactly my use case. I don't want to send out tons of email to my players about stuff they might not be interested in. I do want a place that I can dump interesting things that they can later choose to participate in, low attention kind of stuff. Making a G+ community for five people feels like overkill.
This could be perfect for that.