2: I do. Alliance is better in my experience, however that might be skewed since I do tend to play more on Alliance. A lot less silent groups on Alliance in my experience.
3: I switched to Alliance in Wrath of the Lich King. The lore in the expansion was a lot more to my liking on Alliance side. I think I felt more at ease on Alliance due to the general sense of camaraderie, which was somewhat lacking on my Horde character.
4: Alliance doesn't get their own expansions, though. Blizzard loves Orcs.