When I heard about the possible bonus XP, I was playing my max-level Berserker, so the bar in front of me showed Ascension, which is unaffected by bonuses. What happens when you max that out I don't know - and I'm a long way from finding out. When you're leveling up, the default is Adventure but at max level that swaps to Ascension, since the entire endgame is now balanced around those four classes. These days, EQ2 XP comes in (at least) five flavors: Adventure, Tradeskill, Alternative Advancement, Tithe and Ascension. Well, I say moused over but it wasn't quite that simple. I hadn't heard anything about it but I moused over my xp bar and sure enough, there it was: Server Bonus 100%.
I was happily sorting my bags in EverQuest 2 yesterday (three hours and the job barely started) when I happened to spot someone in chat talking about double XP.