Ok so I'm thinking about implementing a calories burned calculator for running and biking.
I found a good formula: Calories burned by exercise = ((METs * 3.5 * weight in kg) / 200) * duration in minutes.
Where the METs number can be found in the following document from: http://prevention.sph.sc.edu/tools/docs/documents_compendium.pdf
I'm basically posting it here so I don't lose it because I'm gonna go try and crank out about 5 miles now.