With everyone inputting their gas price as part of adding a fill up to be tracked, how hard would it be to add perhaps a zip code / state (for the USA folks) and the European equivalent to our profiles, and then use that data - anonymously of course - to track price per gallon per zip code / state.
People who are planning trips would most likely find this data the most useful.
Also, for the privacy advocates, make the zip code / state data NOT publicly viewable on a person profile, if for no other reason then for the safety of the owners cars on this site.
The problem is with currency conversion really. We let people store their fuel prices in local currencies, but we'd have to do real-time conversion for it to make sense. Also, we currently only track locations down to the country, and not by state/zip, etc. Services like gas buddy are more in tune with following gas prices very precisely.