Auto Scaling Instances
The ability for AppHarbor to automatically scale up or down server instances based on the load of the current servers.
Some additional suggestions on implementing this, would be a max number of instances you will let AppHarbor scale to and notifications if you are approaching the max number.
Would be nice to have instances scale on a scheduled basis. For example, schedule scaling to additional instance(s) only for a few hours (fixed time period) daily.