It's not true that Agile projects progress one sprint at a time. Developers concentrate on the current sprint; nobody else does.

The scrum master and product owner are working at least one sprint ahead, clearing blocks and ensuring that stories are properly defined and estimated.

The testers will be spending at least some of their time on the last-completed sprint (sprint N-1), looking for regressions before it goes live.

The designers will be doing user-testing on the last completed sprint (N-1), helping with implementation in the current sprint, assembling designs ready for the start of the next sprint (N+1), and wireframing several sprints ahead to help with feature definition (N+2).

The strategists will be thinking way ahead, perhaps at sprint N+10.

Others have referred to "time-travelling designers", but everybody on the team is a time traveller.

Except the developers. They stay focused on now.

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This is based on a discussion with Stuart Eccles and Max Williams. Lots of people have talked about 'time travel' as a metaphor, but I first saw it in Jeff Patton's post.