From my experience in coaching Scrum for several teams, while we are doing release planning, I found a problem in two main parts, the first is in user story writing workshops, and the second is in sizing user stories. Both activities consume a lot of time and really exhausting. I think user story writing workshops should be strongly facilitated by Scrum Master to focus on functionality without digging deep into user interface details or techinical details. It seemed proper facilitation will make user story writing shorter and simpler, but sizing still a major overhead.
Sizing problem is actually because it opens again the discussion of story details, plus using the Planning Poker takes a lot of time, in some cases more than one full day, so I was looking for a simpler way to do the sizing.
Last week I attended a Scrum Master course with Hubert Smits, I liked the idea of silent exercises made, we used it to silently as a team rearrange questions written on sticky notes into main pools of “High Priority”, “Low Periority”, and “Done”. We did that as a team of 30 person and without talking, everyone is free to move a question and anyone else can move it again. After a little time of moving the questions, it finally stabilized. It was a very fast and thoughtful way even without any discussion.
As I was looking for a simpler way to do simpler user story sizing, I tried to use the same method in sizing. In the same course, we was a mini team of 6 persons, we wrote the XS, S, M, L, XL sticky notes and without talking we moved user stories around. At the end we did a brief talk about stories we disagree about their size. Generally, if it seems some story is moved as example from Small to large, and by another team member back to Small and the situation continue, we simply put the sticky note upside down to mark it for discussion later on.
Two dayes later I found a clear description to a game of estimation, inventer by Steve Bockman, I liked it so much, it balances between thinking and discussion, also it divided the process into two simpler phases. See: How to play the Team Estimation Game (http://www.agilelearninglabs.com/2012/05/how-to-play-the-team-estimation-game/)