It would be nice if we could define gas "Brands" ourselves in the options and turn that into a drop-down, or even better make it a drop-down with an option of "Not Listed" and allow a one-off hand entry in a separate text field (that only appears when "Not Listed" is chosen).
For "location," can you pull the GPS Lat/Long, or at least pull the approximate ones (so you don't have to invoke the actual GPS receiver and use more power) and either drop those into the location field, or use it to run a map search and spit out an address? The "Mileage" app for Android already is pulling Lat/Long when you do a fillup and while I initially didn't care about the feature, it is actually a really good idea and would allow you to map your fillup history, which could be cool for stats nerds.
One more thing - when importing from a CSV, the option to choose which "car" to apply to would be helpful. I only track a single car as I never drive my wife's car, so my old logs have no vehicle information in them. I can fudge the CSV to make it apply to the correct car, but it would be nice if we were offered a choice of car to apply to if the data has no car info in it.
FWIW, I'm using the pro version, donated a week or two back.