The number in the green rectangle to the left of the station location name is the PlugScore. A station's PlugScore reflects the experience of its most recent users. When a PlugSharer reports a negative experience at a station, its score drops. When a PlugSharer reports a positive experience, the station's score rises. If a driver just wants to check-in and leave a neutral comment, the PlugScore will not be affected.
Remember to check in when you charge up to keep the community updated and raise the station's score!