Tribes: Ascend is getting in on that whole Double XP thing starting tomorrow. The event will last from then up until Tuesday, so you have three days to rack up as much experience as possible and upgrade your face off. Note only baseline experience from each round is doubled, but any other XP boosts will stack.
Normally I'd ignore this Double XP nonsense, but in a Free to Play game, it actually makes sense.
Tribes, for the uninitiated, is a high skill movement-based shooter. Recently, it's gotten Blitz mode and various goodies in an update, so this event is a good a time as any to give it a go.