This seems like a weird correlation but a study has shown that people who mainly use a Yahoo email account spend $110 more on electricity per year than their Gmail counterparts. They're saying this is 11% more electricity and the total difference between Gmail and Yahoo users could power the entire country of Barbados for a year!
What are the reasons for this? One theory is house size: Yahoo users live in bigger houses that use up more power. While this is true, they also seem to be using more electricity per square foot. It could also be that Yahoo users live in colder climates, but that is also not the case.
The real reason seems to be age. Gmail users are younger than Yahoo users, and this affect their lifestyles. Younger people go out more and have less people in their households. Yahoo users tend to be in relationships and have kids.