Experience Orb

Experience Orb is a new feature that will appear in Beta 1.8. They appear as an orb that flashes between a green and yellow colour. They drop when a mob is killed. Once these orbs are collected, they are added to the Experience Bar, it appears the orbs will drift toward the player of their own accord, playing a wobbly popping sound while doing so. (41:00)

History
In a photo of the new lighting system a small yellow (the orb was yellow due to a warm light from a torch) spherical shape can be seen on the left side of the screen, but a day after the photo was published Notch claimed it had an error and posted a new one, this time, without a yellow sphere. In a latter tweet, Notch showed a picture of a beta 1.7 change-list (back then the adventure update was supposed to be in beta 1.7). Although it was completely blurred out and was, at first, thought of as a joke ,but then Notch stated that one of the pictures with the new lighting system and the change list had a secret in them, and people all around the web started speculating.

One place that people discussed it was on the Minecraft forums, where it was discovered that the tabs at the top of the change list that were partly covered, could be decoded based on the 1 pixel tall pattern available in the image.

After a user named "tmcaffeine" successfully decoded, the tabs read: ExperienceOrb.java, changelist.txt, Level.java, Tile.java, HugeMushroomTile.jav(a?), HugeMushroomFeature.(java?), RandomLevelSource(cut) Notch officially showcased it live at the PAX event in Seattle.

Trivia

 * The orbs will be "drawn" toward the player when within 4-5 blocks.
 * Notch has said that Skill Points may be used for buying things.
 * Jeb has said that experience orbs are to be dropped only if the mob has been killed by the player, as opposed to a mob grinder.