Interesting info here:

Patch 1.10 Mage & Talioring Info

Druid Wildheart to Feralheart Upgrade Info

These posts have some details on how you go about upgrading a few pieces of the Mageand Druid tier 0 set to tier .5. The steps are similiar for all the classes sets that I've read about so far.

Also at the bottom of the Mage post you'll see some nice info on new tailoring patterns (Enchanting and Herbalism bags).

Can somebody please explain to me what this tier stuff is?

Thank you for your patience and kindness in advance :)

They are sets of armor. Each class has several sets, or tiers. Tier 0 is the 'weakest'. Tier 2 is the best. Each Tier gives you bonuses if you are wearing multiple parts of the tier.

Tier 0 is gotten through drops at the high 50s instances. BRD, Scholo, etc.
Tier 0.5 is gotten through quests that you can do to improve your Tier 0 stuff. This is the big change in patch 1.10
Tier 1 is gotten through drops in the Molten Core
Tier 2 is gotten through drops in BWL

So for priests, the tiers are

Vestments of the Devout (Tier 0)
Vestments of the Virtuous (Tier 0.5)
Vestments of Prophecy (Tier 1)
Vestments of Transcendence (Tier 2)

Some other class sets:

http://www.wowwiki.com/Warrior_sets
http://www.wowwiki.com/Paladin_sets
http://www.wowwiki.com/Rogue_sets

Ok so to get to 0.5 I have to have the Tier 0 armor, which is the shadowcraft armor for rogues. Damn, I was really hoping to get out of that shadowcraft stuff but the 0.5 Dark mantel armor is really pretty cool.