Man... I started a Druid last Sunday and casually played all week... I am 39 leveling as Feral and have no problems with anything 46 and lower... it is insane how fast it goes right now. Last night I got on and was level 33... went to bed at 39.5... it is just silly how fast you can kill and with no down time at all. The longest times between levels comes when you want to go train. I understand this may slow down with Cataclysm, but for now it is just crazy fast.
Gets faster with LotP. Can't remember what level you can get it at though.