Adding a field to set a Maximum value for duration graphs on the Statistics page and the Build Stats gadget would allow for more useful graphs when you have builds whose durations are outliers.

For example, you have 100 builds in your history, 99 of them are under 10 minutes, but one, because of some issue is 100 minutes. Your graph will essentially be a flat line near the bottom with a single spike. This makes it very hard to see trends when your data is 'polluted' by some outlier builds.