Instance attunement refers to the process of gaining permanent access to an instance. The term comes from one of the first of such quests created: "Attunement to the Core." Many of the endgame instances require you to complete a quest or obtain a certain item to allow entrance. (from wowwiki)

heres a link to the TBC attunement chains (click the names to lock the attunement path)

World of Warcraft Europe -> Info -> Basics -> Burning Crusade Attunement

a complete list of attunements can be found here

Instance attunement - WoWWiki, the Warcraft wiki

Atunments are kinda fun but get boring when they are just plain old farm this save me get me that.

I remeber when i was trying to complete BWL attunement like crazy, then someone told me it was always open >.<
Attunements are lotta fun, not to mention they reveal some of the background and lore.
Just one thing. The TBC instances/raids that normally require attunements to be accessible, still require here in the den? or like the BWL they're always open (Hyjal !) ? Im just asking this cause i didnt have any time to play after it was upgraded to TBC (gonna start playing tomorrow)

that kinda work is far in the future as currently all database groups are focused on getting the basic spawns etc right. plus support in the core is lacking for quiet a few things. most of this has to be scripted and mangos dev's arent going to add anything script/script related into core