Moorguard posted the answer to the question everyone has been asking. You have been asking right?
How Does Bonus Experience Work?
Some players have noticed that two grouped characters of the same level can defeat the same number of opponents and have the same number of deaths, yet they advance to the next level at different rates. This isn't due to a bug or race/class bonuses, but rather because of a feature called Vitality which augments the amount of XP you receive.
Vitality was added to the game during beta, and our plan was (and still is) to add a visual UI element that shows your current Vitality status. Unfortunately the visual portion wasn't put in place during beta, and other UI tasks became a priority over it.
While it's a rather straightforward idea, the current way it works has led to confusion and concern on the part of players who have seen their experience gain change for no apparent reason. We definitely feel it's important that you understand things that relate to your character's advancement, so we'd like to offer this overdue explanation.
How Vitality Works
All characters gain a chunk of Vitality every hour, on the hour, and keep accumulating it until the maximum amount is saved up. Each time characters gain experience, they use up a portion of their Vitality and receive a bit more experience than usual. When the character runs out of Vitality, he or she no longer receives bonus experience.
So what is the confusing part? Well, currently the Vitality bonus is received at three different levels. At high Vitality, you're receiving matching experience for what you earn. At medium Vitality, you earn half as much bonus XP. At low Vitality, you earn one quarter bonus XP. Because each level of Vitality accumulates separately, it is possible to jump from one level to another when a previously empty pool accumulates enough bonus to draw from it. Unless a character stopped earning XP until their Vitality pools were completely full and played until they were completely empty, the bonus wasn't being awarded in a way that seemed to make logical sense. The lack of a gauge showing how much Vitality you have only makes things more difficult to understand.
In order to clearly show the effects of Vitality, we're going to switch to a single pool that gives a consistent amount of bonus experience. We also plan to add a UI gauge that shows how much Vitality you have left. This way everyone will be able to easily see how your XP is affected.
Vitality was designed to benefit everyone, whether you only play a few hours a week or whether you play many. If someone only spends a few hours here and there earning experience, they will spend a lot of their playtime earning bonus XP. Playing so much that you constantly use up all the Vitality you earn means you'll get every bit of potential bonus XP coming to you. There's no need to quit playing if you run out of Vitality, because you know you'll get a new chunk of it at the start of the next hour.
Vitality applies not only to adventuring experience, but to quests and crafting as well. Any activity that earns XP will make use of the Vitality bonus, assuming you have it available.
The goal of this system is to provide a benefit to everyone, regardless of play style or the rate at which you choose to advance your character. We didn't intend for it to seem mysterious and confusing, so hopefully now it's a bit clearer. Once the system is totally in place, it will be much more straightforward and easy to keep track of, which is how your character's progress should be.