(first of all, sry 4 my bad english )
all my 4 shamans have engineering and its awesome!

in pvp its a very good extra bust every 45sec
(you cant use the frag belt in arenas but it's very helpful in battlegrounds, 0,5sec casttime for a 3 sec aoe stun and you can use it when you are running)

if you are an engineer you can equip the battlemasters trinket (111spellpower+3385life/15sec on use or the newer one with 160spellpower+4600life/15sec on use) and the titan-forged rune of audacity (111spellpower+ removing all cc effects), so you have not to "waste" a trinket slot for the resilence+spelldmg on use trinkets which have a 2min cd

yes, with JC or another profession you'll have more constant dmg, but in pvp we need burst and ... ehh .. burst! and with the hand-mounted pyro rocket you can have extra burst every 45sec (no GCD and 45y range!!!) with more burst your enemys die faster, and if they die faster you get less dmg from them.

if an enemy run out of range with low hp ... just pwn him with teh imba 45y flameshock+pyrorocket combo!
if someone is low hp, shocks,thunderstorm and all the rest is on cd ... just pwn him with ya pyrorockets!
*** engineering *** buy NOW *** it's amazing! *** be George W. Bush in WoW, bomb you enemys out of the arena *** only with pyrorockets *** try it ! ***