The version number. It’s so Smexy.
Nah, but seriously the bugfixes tend to be pretty nice.
That said, there’s generally a lot of cool stuff in each new version.
That said I still prefer the things called Carboys over Gallon jugs. They just sound cooler. Then again, I suppose more people will understand Gallons as a unit of measurement than a carboy. (Seriously, you’ll hardly ever find carboys of anything over here in the EU.)