You know a beverage has gone mainstream when it starts getting requested on airplanes. I recently heard passengers requesting Coke Zero while on a JetBlue flight to San Diego. The answer was no - only Diet Coke was available - but it told me that Coke Zero popularity is on the rise. And the stats look to back that up - Beverage Digest reported (PDF) in March that Coke Zero volume was up 37.5 percent in 2007, when almost all of the brands in the top 10 were declining. Maybe the airlines should take note (looks like some restaurants have).