This takes some believing, and one has to assume that the Nokia E6 in question was in 'offline' mode some of the time (not least because of all the air travel), but a guy from 'The Polish Jules Verne Society' has documented, in video, his week long trip around the world on one charge of the BP-4L 'hero' battery in his Nokia E6. Reporting on the trip (plus all the video footage) was done on the E6, too, with battery readouts superimposed later in editing. He got back to his starting point (in London) with "0%" left but the phone still worked.

From the original page on YouTube:

Welcome to our trip around the world. On the 140th anniversary of the world famous “Around the World in 80 Days” journey, Nokia E6 faced the challenge of Jules Verne. Except for one thing. Instead of 80 days we have 1 battery and no charger.
General Information

Thanks to an inspiration of a Julius Verne’s fan we have one of a kind chance to show to the world all those beautiful cities which Phileas Fogg has seen during his travel. We will document them via posts, photos, movies and recorded phone talks. Join us on Facebook, Foursquare and Youtube. Become a witness of this great adventure.

Very cool experiment indeed. Using the E6 as my main device I was getting between 2 and 3 days life on each charge. Anyway, here's the English language version of the Nokia Poland-sponsored video: