There are so many APIs these days, introducing some Arduino functionality might just be crazy enough to make sense.
Imagine, you're trying to manage your weight.
You're using something like a Withings Smart Scale and you have access to its API, you've exported and logged your body's fat content and weight trend over the days/months, and you can tell if it's going up or going down.
Perhaps you're also using MyFitnessPal where you're logging how much and what you eat each day and have access to its API, you perhaps thought you were doing well in keeping this in check.
And for fun, you have your Arduino, connected up to your treat box. It controls whether or not it's open or closed.
See where this is going?
From a bit of logic, from trends in your API, it communicates with your Arduino to decide whether or not you should have that treat today. Maybe it could be detailed enough to keep a log of what kind of treats are in there and how many calories they are, and integrate with your fitbit api to determine if you've burned off enough?
It's that level of smarts and intelligence from integrating things together that perhaps, are just crazy enough to be sensible.
What're you working on?