Barely a day after going live, Zul'Aman has been conquered and Zul'jin defeated. EU guilds Curse and Death Wish were the first to report kills, but by this point nearly the entire loot tables for each boss have been reported to World of Raids.
From what we've seen so far, the loot is between Karazhan and SSC / TK in terms of quality, at item level 132. In addition to a single epic, each boss is reported to drop 2 Badges of Justice, with Zul'jin dropping 3. These can be redeemed for a new sets of gear that supports nearly every spec at costs of around 50-80 badges.
It seems that the encounters aren't especially difficult, but most guilds that have attempted it seem to be geared out in t5-t6, so we'll most likely have to wait until it goes live before reports of Karazhan geared raids come in. Right now it looks like the initial encounters are slightly beyond Karazhan level in terms of difficulty with the additional aspect of time limits, which add additional epic rewards when fulfilled, in place for more advanced raids. The time limit rewards are the same item level as the actual boss drop loot though.
edit: I apologize for not making this clearer, but Meet Your Makers (who are reported at World of Raids) and Curse are the same guild. Also, while I only mention the two big guilds reported by WoR, many other guilds have cleared ZA at this point.