From the webpage:
The same API that powers Forecast.io and Dark Sky for iOS can provide accurate shortterm and longterm weather predictions to your business, application, or crazy idea.
We’re developers too, and we like playing with new APIs, so we want you to be able to try ours hassle-free: all you need is an email address.
First thousand API calls a day are free.
Every 10,000 API calls after that are $1.
It could be useful/amusing to merge personal weather observations based on profile characteristics.
Like a recommendation system except for how you are going to experience the weather.