Do you run the same gear setup for every bracket? I find myself swapping in items.

I'll start.

2v2 (Paladin/Warlock)
I swap in my blue GM Dreadweave Gloves for 50% Fear pushback resistance.

3v3 (Paladin/Warrior/Warlock)
I'll use Felweave Gloves for the 50% Searing Pain. Some people will say you should use the Fear gloves, but with the spec I'm rocking, we just overwhelm people with damage in this bracket. The constant damage works out better and when Warriors realize they can't stop me from spamming Searing Pain, it gets kicked, letting me switch to Drain Life.

I wear the same gear for 5v5s but I've got two alternate sets. One is sort of a "work in progress"

Shadow Resist: I have a +70 SR set which swaps in a cloak, helm and neck.
Tanking: I'm building a (post 2.1.0) +1100 armor set which is a cloak and 2 rings.

2on2 Paladin+Warrior (im the warrior), Realmpool #2 with 2361

Gladiator set full with +8 Str / +4 Str 4 Crit DPS gems - standard
Shadow Resi Gear (Cloak+Helm+2 Rings+Amulet+Shoes) - against WL+Shadow and Disc-Priest+WL mainly
Frost Resi Gear (4 Slots) - against double frost mage

Paladin always wears the same gear.

Only thing i use besides standard gear is http://www.thottbot.com/i4984 for huntertraps.

My 2on2 team relies a fair bit on cc/burning the enemy team before they burn us, resistance wouldn't really help that :/

Dreadweave gloves for Arenas (in my Aff/Demo spec) and Felweave and various other crit items for Battlegrounds (in my Destruction spec). Pretty much the same gear otherwise. I actually have ~14% crit in my Aff/Demo spec.

I mostly swap out trinkets. HP trinkets like the engineering ones or the argussian compass, dps trinkets like renataki's, utility trinkets like tidal charm(when one team's healer is giving us a hard time, for example).

Sometimes in 2v2's with my paladin, if it's a drawn out match, I'll FD and switch into some PvE gear, since it provides much better mana regen, but generally I don't find it worth it to wear anything other than my usual gear.