HOW TO KEEP TRACK OF YOUR GOOGLE+ DISCUSSIONS
You know you have a “Send a message” button on Google+ which you can use to start conversations with people. You can of course just make a private post and * +mention them* to the post and accomplish the same thing. (Or even use the “Say hello” button when someone circles you back).
The sad part is that sooner or later as you share more posts, you’ll find it harder and harder to get back to that conversation. What I do is I have created an empty circle called “Conversations” and when I make a private post to talk to someone, I share that post also with my empty Conversations circle and whenever somebody starts a private conversation with me, I share his post to my empty Conversations circle.
This way, I can always get back easy to my conversations by going to the “Conversations” circle’s stream. Of course… for the posts that weren’t initiated by me, I have to check them manually by going to them. But I can always find the links to those posts in my special circle.
Another way to keep track of your Google+ discussions is by using the Gmail filters & labels version explained by +Michelle Marie here: https://plus.google.com/114618043230336563405/posts/EDYmMgevoZ1