An example of the output it produces:
Comparing reserved instances to running instances...
m1.large:
us-east-1b 1/1
us-east-1c 1/1
us-east-1d 1/1
c1.medium:
us-east-1a 4/4
m1.small:
us-east-1a 1/0
--
0 unused reserved (good)
1 unreserved running (bad)