New patch today (4/25) pushed out a Jimmy McWeaksauce to PTRs that lets anyone with honored+ rep with VE get attuned/ported to Mount Hyjal. On live to zone into Hyjal you must kill Vashj and Prince Kaelthas (so no one on live is keyed yet). Patch was 38 megs by the way, fairly large (the original 2.1.0 patch was something like 200 megs). Lots and lots of little bug fixes, like hunter, alliance epic mount wingsflaps, etc.
Hyjal is in Tanaris obviously, one of the CoT wings. When you zone in, you are in a small cavern with a raid entrance (another zonein), and two gates "Night Elf" and "Horde". There is also a vendor that sells 3 pages of gem designs, and the T6 vendor (!).
You can see the gem vendor loot at
http://www.mmo-champion.com.
When you zone into the raid instance you start out, as Alliance, at a small alliance base with lady Jaine Proudmoore and lots of 70 elites, including horsemen, dwarf riflemen, NE priests, bloodelf Sorceress' (?).
The starting area is standard alliance structures, few towers and buildings, think Theramore. You start the encounter and rush out to fight Undead - a few 70 elite abominations (naxx) are the first encounter.
Don't see a map yet, not sure if its because of a mod or there is no map for Hyjal ingame.
No obvious zone-out point in Hyjal. Graveyard is standard CoT GY, so a 3-4 minute run. Fighting the first groups now, more later.