I used Gas Cubby for years before Fuelly took it over. I was not in love with the old interface, but it was comfortable and I knew how to enter and find things. It fit my workflow. The new version assumes that all entries are made at the pump right after fueling; that a few data items are vital and the rest irrelevant; and that a flashy interface beats a utilitarian one. If I could transfer my data safely I would stop using the new version, but for now Im stuck (and hoping Fuelly wont lose my data, AGAIN). Not recommended.
JHerlocker about Fuelly: MPG & Service Tracker, v3.0.11