We use it to replicate production traffic to our staging and testing environments at https://reverb.com. It's an incredibly useful and functional tool. We've used it to shake out exceptions from our blue/green deploys as well. For instance when we migrated from Rails 3 -> 4, Gor was paramount to shaking out some pretty nasty bugs by replicating prod traffic from the Rails 3 cluster to the new Rails 4 cluster.

Gor is awesome!