I can confirm that the exploit used to enter Hyjal pre 4.03 can be used to enter Uldum, Hyjal, or Twilight Highlands.
1. Have a party composition of a two priests, warlock, and anyone else who wants to come. Preferably enough to summon the priest multiple times as you attempt to figure out where the <No Man's Land> debuff shows up.
2. Turn on your Scrolling Combat Text, and all of the options in between.
3. Use the priest levitate wall climb (you simply cast levitate, then walk and hug the walls) to the outskirts of any given zone. Have a priest inch towards the inner area of the zone until he gets the debuff <No Mans Land>. Mark the point, either in memory or with something you can drop, like a Moll-E or Jeeves.
4. Summon the priest back. Challenge the priest to a duel. The priest will mind control you, and move you past the <No Man's Land> point. You need to watch your SCT, and as SOON as you see the <No Man's Land> debuff show up, you need to leave the party right away. Right click your portrait after the duel begins so you can be ready to leave the party immediately.
5. The last people across the debuff marker should be the two priests, so that they can duel and mind control eachother across.
Enjoy exploring these zones two weeks before they're intended to be! Don't exploit the nodes/greens too much!
P.S. - Rares are up, they do drop blues, and you can collect all the flight paths/work towards Explore Cataclysm achievements. Try to keep it on the down low though, as if you are reported, you run a risk of a temp ban/removal of achievements or loot.
In Action
http://img221.imageshack.us/img221/4849/uldum403a.jpg