As promised, I explored the new Inscription profession in the WotLK beta. First thing to say is that it isn't finished yet. You can level it up to 125, and then the trainer only has one more recipe for skill level 250, but you can't reach that because you don't have the intermediate recipes. Obviously a lot of recipes still missing. From the promised recipes to modify spells there is no sign yet.
So, what is Inscription? Inscription is the tradeskill to make scrolls. You can make the regular stat-buffing scrolls, but also some special scrolls like the Scroll of Recall, which works like a second hearthstone. Useful! Furthermore you can make blank scrolls for enchanters, on which the enchanter can then place his weapon or armor enchanment and thus make it portable. This finally allows enchanters to put their enchants on the auction house, which is a huge improvement.
The first recipes use Peacebloom and Silverleaf, the basic herbs from the newbie zones. The recipes after that use pomace, for example Alabaster Pomace. The pomace is made with a new skill, milling, which you get when you learn inscription. It works just like prospecting for jewelcrafting: You click milling, then you click a stack of herbs, you lose 5 of the herbs, and gain 2 to 3 pomace. There are less different pomace than there are herbs, so Peacebloom, Silverleaf, Mageroyal all give Alabaster Pomace from milling. Finally a good use for those more common herbs nobody needs.
The pomace is turned into ink, and the ink plus parchment gives a scroll. The parchments are available at the inscription goods vendors. For Alliance I found the grand master inscription trainer in Valiance Keep in the Borean Tundra (you get there by boat from the new Stormwind Harbor), but the inscription goods vendor was in the mage tower at Amber Ledge. There was both a vendor and a trainer at Dalaran, but the trainer didn't seem to be working yet, although that was difficult to say with the horrible lag that place still has.
It is hard to say yet whether Inscription will be useful, as it is yet in a very unfinished state. But I'm looking forward to exploring it some more in some later build.