Where I work we practice scrum-driven agile with 3-week iterations. Yes, it'd be nice if the iterations were shorter, but changing that isn't an option at the moment.
At the end of the iteration, I usually find that the last day goes very slowly. The actual work has already been completed and accepted. There are a couple meetings (the retrospective and the next iteration planning), but other than that not much is going on.
What sort of techniques can we as a team use to maintain momentum through the last day? Should we address defects? Get an early start on the next iteration's work anyway? Something else?