Dungeons and gearing up in Cataclysm

Just a quick glance at Wowhead's data mined information to give us an idea of what to expect gear-wise when we begin our journey to Tier 11.

80-82 Dungeons:

Blackrock Caverns
Throne of Tides

These two dungeons will be the first dungeons you will encounter at level 80. Both drop item level 279 blues in normal mode. Yes, that's 2 item level points above your precious Heroic ICC gear. However, they might not be worth the upgrade.

For example:

Sanctified Shadowblade Pauldrons Rogue T10 ilvl 277
Caridean Epaulettes Which are a 279 leather shoulder drop in BRC.

Based on the normal stats alone, this is not a worthy upgrade. You'd pretty much have to be coming into these dungeons in ToC normal 10 man gear for any of this to really even be considered as an upgrade.

82-84 Dungeons:

The Stonecore
The Vortex Pinnacle

Now these two dungeons drop 316 item level blues in normal mode. A whopping 36 item levels over Heroic ICC gear.

To compare:

Helm of Numberless Shadows
Sanctified Shadowblade Helmet

The raw stats are better. However, the new helm has no gem slots, needs to be enchanted, and the green stats may not be exactly desirable for you. But, these items are worth consideration, and will likely be an upgrade for most gear under 277 ilvl from Wrath.

84-85 Dungeons:

The Lost City of Tol'vir
Halls of Origination
Grim Batol

These dungeons drop item level 333 in normal mode. A very large leap up from our 277 item level gear. So let's compare.

Hieroglyphic Vest
Sanctified Shadowblade Breastplate

Finally! Something that is clearly an upgrade to 277 gear. Set bonuses and theory crafting aside, this would be a very considerable upgrade.

I believe it is safe to assume that you could entirely bypass using dungeons at all until level 84, and then it might be a good idea to run a few normals to familiarize yourself and grab a few upgrades before leaping into Heroic level dungeons. It's also entirely likely that Blizzard will have an item level requirement for Heroic LFG queueing like they have done with the recent 5 man H ICC dungeons (HoR, PoS, FoS).

Another note, please remember that hit rating, expertise, armour and dodge ratings will need to be increased in order to actually damage and do your job. Also don't forget reforging! So keep these things in mind when you pass on something. If you can't clearly say that piece of gear isn't worth it, need on it and take it.

You will certainly need to use your JP to purchase vendor upgrades, and run Heroics in order to attain a desirable item level to jump into the first raid.

TL;DR: 80-82 dungeon loot = meh, 82-84 loot = on the fence, 83-85 and beyond = Upgradez! Also, make sure you do your dungeons.

Just for you, a list of the first Cataclysm raids.

Baradin Hold
Blackrock Mountain: Blackwing Descent
Bastion of Twilight
Throne of Four Winds