We would benefit from being able to deploy and/or promote to more than one environment at a time. Once the release has been succesfully tested on a test site we then have to deploy to each of our production sites one after the other.
I expect that multiple deploys is going to have to be done as a queue of tasks, with all the attached issues like viewing the task queue, editing the queue etc. so I can see that it could be quite involved. Having said that, a queue of deploys would be nice as that could extend to scheduling of deploys (for example over night).