WoW's crafting system has always been relatively straightforward. Collect mats, press button, receive item. This lies in contrast to crafting systems from other games, which may contain mini-games, convoluted learning systems, or varying levels of success in production. In WoW, you can't even fail at making something; if you can make it at all, every attempt will result in an item, and they're all the same (aside from some recipes with random enchants. This fits in with WoW being on the simple side for MMOs (simple to learn, that is; often difficult to master).
Jewelcrafting in LK is going to shake that up a little bit. There will be a quest available to jewelcrafters that gives them a chance to craft a "perfect" version of an uncommon-quality gem when cutting it. For the first time, it's possible to have a critical success from crafting in WoW. It looks like the perfect versions of gems are positioned precisely between the uncommon and rare versions of a cut, in terms of stats. For instance:
- Delicate Bloodstone: +12 agility
- Perfect Delicate Bloodstone: +14 agility
- Delicate Scarlet Ruby: +16 agility
- Delicate Cardinal Ruby: +20 agility
So far, Gem Perfection appears to work only on uncommon-level gems, not on rares or epics. I also don't know what the chance is of cutting a perfect gem instead of a regular one. It's a nice change, and a little something extra for cutting those buckets of green gems on the way from 375 to 450. Would you like to see more critical successes in other crafting professions?