Another suggestion for the clever girls and boys at RunKeeper: why not introduce a Body Mass Index measurement?
Next to the weight and body fat (BF) measurements – which are indeed ideal quantities to report on – a private BMI ticker would be significantly interesting. This private ticker could be colored from green (value from 20 to 25) to red (less than 20 or higher than 30) and shades in between.
Throw in enhanced reporting on both weight, BF and BMI, just like the FitnessReports on Body Fat Percentage already available today. The icing on the cake.