This is a great idea! In fact, it is almost the answer to a prayer for me.
I don't live near my family. My younger sister is always calling to complain about what my brother-in-law says to her husband at family get togethers. In fact, it's gotten so bad, that my sister doesn't even want to go to holidays with my family.
She calls me up to complain for hours on this issue, knowing that I also had problems with him when I lived there (one reason I left!)
I've found that when it comes to my sister, she can get me into rehashing the past to no good end. I feel terrible after I talk to her.
Now I can tell her I've taken a vow of "no complaining" for a month. Wont' be much fun for her to call and chew my ear off that way!