I have commented several times on the 2-weekly cadence that we follow at the certification team, but I haven’t gone into much detail on our 6 monthly cycle. We have just completed the Natty cycle (normally release date + 2/3 weeks) and we are about to start our Oneiric one.
6 monthly cycles help to plan achieving longer goals that drive the user stories implemented by the team in each iteration/sprint. During Natty, we had a loose coupling between these two. I regularly (once a month) reviewed the progress of the Natty backlog and made sure that nothing was falling through the cracks. Despite the good completion rate in Natty, it was more of a case of the user stories forming the Blueprints (6 monthly requirements) than the other way around.

For Oneiric, the certification team went into UDS-O with much better defined blueprints. This has not only resulted in better sessions, but also on well defined backlog. Clearly, there is no much point trying to tight down what we will be doing in 4/5 months, so user stories towards the end of the cycle are vague and fairly large. User stories for the next 2 months are better understood and described.
We have been collecting velocity data for the last few months, so by asking the team to roughly size new stories and review the sizes for the “next_iteration+1”, I hope to be able to build a burn up/down chart over the next few weeks! I will keep you posted.