I put in the 300th tank of gasoline in my 2005 Scion xA on Sunday (since buying it new almost 6 years ago). It was a tank over 500 miles, and the first tank over 500 miles was back in February, so for at least 10 months this year, I have driven farther than 500 miles on a tank.
I think the warmer weather is directly correlated with higher FE. Daytime highs are still in the mid 60's (F) around here. The ground is not frozen, yet...