Anecdotally, I’m running Kubuntu on a Dell 7280 with a 4 cell battery as my personal computer, which gets an hour or two of websurfing and home network experimentation per day, and I’m having to charge up once or twice a week. I dunno how that stacks up to other devices or distros, but I really barely think about my battery.
It’s not as impressive as some of the other projects mentioned here, but there was a one-year hiatus during the filming of Cast Away to allow Tom Hanks to lose all (and more) of the weight he had gained for the first part of the movie. His beard and tan were earned honestly during that time as well.