Comment 2 for bug 666544

Robert has some suggestions about implementation for this in <https://lists.launchpad.net/launchpad-dev/msg07250.html>, specifically towards getting a slice of users.

So there could possibly be two different scopes: consistent x% of sessions (including anonymous users), and separately a consistent x% of users. The difference would be in the first case logged-in users would possibly see different behaviour from one machine to another. That may not matter.