Steps:
- Equp unenchanted gear with primary stat.
- Join skirmish
- Switch gear for enchanted gear, enchants will be added to your stats.
- Rinse and repeat, you'll observe the "added" value of your stats is saved and every time you re-equip gear you'll get an additional bonus.
This bonus applies to any form of instanced pvp, not sure about world.
Video and more detail to follow.