We have a staging environment, but its really only used for really big changes that might need to be experimented with before being deployed. We can also deploy a branch to a single front end to observe how it behaves with a subset of the traffic, and roll it back quickly if needed. Also, most large user-facing features are released as "staff-only" first, so we as GitHub users are able to play around with it for a few days or weeks before enabling it for everyone.
No. There's simple conventions for adding feature flags (user.some_feature_enabled?). Features are enabled and disabled by changing the code and deploying. This works because deploying new code is fast.
We do use Rollout (https://github.com/jamesgolick/rollout) once in awhile. Most of the time, we like having the history of flipped feature flags in the Git code though.
