Screenshots -- an informal survey on Twitter as I wrote this Breakfast Topic tells me that the only time players today seriously employ first-person view in World of Warcraft is when they're taking screenshots. Quite a few smart alecks and their guilds report toying with first-person view during certain raid encounters; as one of the twitterati explained, "It, uh, did not end well usually." In a game of encounters based on moving out of the fire, the loss of situational awareness you'd suffer in first-person view is simply unconscionable. In fact, we recommend that you scroll back still more -- way, way back is the smart way to roll.
Other games often include certain encounters or tight locations in which scrolling into first-person view is most effective. When pressed, some WoW players admit to scrolling in when they're in an especially tight spot -– say, to snag the bag of loot on the pirate ship on Timeless Isle. Still, it's not a tactic players employ with any real frequency.
I have to wonder if there are players out there using first-person view for roleplaying or business around town. After all, wandering about with your UI entirely turned off can lift a veil to an entirely new way of looking at Azeroth, so why not consider popping into the head of your own character? Do you use first-person mode for anything other than screenshots?