Get for all the Haste off-set pieces you can get. Tier only has crit on it so it's a decent trade off.
As for comp... don't know. I only do Arena for fun and i do it as Destro with an Ele Shammy and a Disc Priest. If we get our minds to it we pretty much can't be stopped(Destro + Ele + Heroism + Fear, Hex, Stun = one dead anything). But smart play from any comp will butcher us because... we suck at arena
I am still iffy on crit for pvp, due to resilience impacting on the relative chance to crit someone quite substantially.
Come cataclysm and the removal of that effect from resilience, and we will have to rethink that substantially.
That and the inability to get quite so much haste easily, could see crit playing a much bigger role.