the issue while levelling is crap but not unsurmountable, the bigger issue is in outland where both factions inhabit every zone, especially when you are level 70 like i am, I now need to farm quests for rep, gold for flying and more, and its virtually impossible because wherever i go there is at least 10 horde compared to me.
I already am levelling a horde toon as well, currently 30+ just in case things do not imporove, then i will pve on my horde toon and pvp as alliance. I would rather not have to do that though, but not fun when there is not a huge amount of people at 70 on alliance, hard to get groups, cant do elite quests, cant farm rep outside of dungeons, cant quest for gold without being ganked non stop, meanwhile as horde you can rest safe in the knowledge that you can pan the camera around 360 degrees and see multiple other horde no matter where you are or what time of day.