My experiences have been nearly universally positive. See other MBers every now and then and always give em a "greetings fellow MultiBoxer".

The closest thing I ever got to some hatin' was one day in Dalaran, there were a few other horde being bemused my three toons with very similar names all in the same guild.

Maybe I'm SLIGHTLY less obvious because I tend to run a pally, a priest, and a mage, so it's not the troop of identical toons a lot of folks see, or maybe it's just that folks don't care as much on Rexxar and/or PvE servers.

Whatever the case, I've had more than a few non-multiboxers stop and say hi or ask how I do it, or just (not blowing my own horn) marvel at how I can manage to tank/dps/heal all at once.

No idea how the Alli side is over there though. Never really had an issue on Spinebreaker (PvP) back before I transferred over (to run with a bunch of RL friends, and I hated PvP)