On my team we have about 5 developers and 3 QA testers.
Our sprints are 10 day sprints but our work as developers is due on the 6th day so that the QA testers can have 3 days to test our completed work before our biweekly release.
I feel like the system is very inefficient and really limits the work we can do as developers since we only have 6 days of development followed by a few days of thumb twiddling since there aren't any more user stories groomed yet.
How does everyone else do it?