I'm on Cairne as Horde as well (current group is not in the Zerg - haven't decided if my buddy and I are going to just make our own or not for fun) and while it's cool being on a new server there are a couple of downsides:

1. The economy sucks.

2. Most of the population sucks. I've been followed, gotten a zillion tells of "wtf?" and "dude who's following you?" and more constantly every time I'm there. Sure, a lot of them are just curious but some are annoying. I've already had to /ignore a couple of folks. And if I had to guess I'd say that 90% of the people sending me tells are under 18. No offense to you under 18 folks but DAAAAY-EM, you can be annoying!

3. Large lowbie population - which makes certain quests more difficult since you're competing for spawns/collections/etc. This isn't insurmountable since most of them don't know what they're doing yet so if you know your quests you can still cruise through but it does slow things down at times.

There's a number of multiboxers there though so my guess is that it will become multiboxer friendly over time as people get used to it.