Pretty much zero, since most of the really useful items made via engineering are not usable in rated pvp matches. Having said that though, I wouldn't let it deter you from getting it for other forms of pvp if it is a profession you're interested in.
springs+tailoring proc when synced up can make for some good burst on a kind of low cd, tailoring proc is something like 45-55 sec cd, and the springs are 1 min on use cd. Can make for good unexpected burst.
If the engi glove enchant could be used with on-use trinkets, maybe it would be worth something. As it is, your gloves will rarely sync with CDs unless you're rolling with the proc trinket as opposed to the on-use one.
Aside from joking around in BGs, Engi's fairly weak as a PvP profession because of it's limitations.