Flying really doesn't break immersion for me. I agree with the person above that teleports make the world seem a lot smaller than being able to fly around a zone. If anything, flying allows you to explore and see places in the game from a different perspective where you otherwise wouldn't pay your surroundings any attention. It's just fun.

I do wish we had flying mobs that could swoop in and aggro us in the sky...might make it easier to come up with a working set of rules for quidditch now that we have that awesome broom mount if the actual game mechanics allowed for it, sort of like that old mob soccer game back in XI...
(I haven't actually tried the broom out in HW areas yet, just assuming it flies because flying broom.)