I was bored and felt like some exploring, so i logged on to the WotLK beta and on to my death knight (lvl61) and went to northrend with the boat from stormwind harbor. When i got there i used Path of Frost and started to run sotuh. I reached the edge of the maelstorm when i suddenly started to fall down and died like you do when falling of the edge of outland. So i had to release and got to the GY in the crossroads (im ud btw).
So it seems like there's no fatigue in northrend or you can avoid it as a deathknight.
That's the only picture i could get, cause when i died i couldnt open the map.
edit: i did some test in azeroth and there's still fatigue, so there's probably something with northrend.