It's come up a few times, such as
http://www.fuelly.com/forum/224/Fuelly-API and
http://www.fuelly.com/forum/318/API-for-fuel-ups. Are there any news about this? This request will keep coming up in the future, especially with smartphones becoming so prevalent now.
One of my friends uses FuelFrog, and it has the unique feature of watching a user's Twitter feed for fuel-up statistics, which would be another cool way of updating remotely.