Right now im a 454 engineer, still wearing my goggles, T7 gets passed on me because it's a bigger upgrade to others and i havnt seen thane's helm in naxx10 yet, ive been wanting to drop eng. for Jc but ill be downgrading my helm to titansteel or arcane-shielded (if it drop *crosses fingers*), the gems and the monarch crab are huge in Jc, but im not sure its worth the downgrade, or should i wait for thane's or T7, which may be a loong wait.
I got several reasons,
1.Figurine - Monarch Crab - Item - World of Warcraft best tanking trinket
2.solid dragon's eyes
3. eng. bores me now, it used to be fun and i could careless about the motorcycle, 12.5k in vendor mats is retarded, it trivializes making the bike, anyone can farm gold
4. Im tired of buying gems off AH every upgrade lol
You may find yourself continually switching if your goal is to min/max your profession for your role. Blizzard's intention is to not have any one profession be the best for a particular class/role. I wouldn't expect the current situation to last the entire length of the WotLK expansion, just as it didn't in TBC. If your goal is simply to make money, JC is a very good one. So is inscription as I'm finding out on a new alt I started. If they had inscription in the game way back when, making gold on a new realm would have been a breeze.