There isn't an easy option for ilvl 353+ shoulders beyond pvp-crafted stuff. I wouldn't dare to use PVP stuff to try and heal/tank in PVE (in a cata setting)
That can really sink your ilvl if you're stuck with a 305 from quests. I bought my mage the 390 pvp shoulders because I couldn't get the 373's to drop outta HoT heroics.
It's kinda moot in MoP Because they're moving back to not charging itemisation allocation for PVP stats again (sorta like they did in BC.) I don't think it'll be a problem this time (They switched it because PvE-ers were pvping to get the latest tier's pvp weapon, which was comparable to weapons that drop in top-end-content) Entry level PVP gear is pretty close to what you'd get in heroics, plus resilience.
They generally have a decent "catch up" rate on getting OK gear from wherever. with LFR weapons, PVE'ers won't really need to pvp to get their hand on a decent weapon. (weapons are actually still being penalized anyway.)