In general magic/arrows home in on you, though they can still be dodged or blocked, depending on the range, etc. IIRC the homing effect was effect was reduced in the latest patch/release, at least on the easy difficulty level (I played the US Xbox release).
The rapid fire missiles are the normal attack for some flying opponents. I don't recall how much the home in on you, though. I took a fair bit of damage from one at the start of the fjords, while I was pretty much stationary taking out a couple of the anti-dragon defenses with Fire Sphere. While I was moving I don't recall them being a huge threat, though (especially since I leveled in the fjords before taking the battle tower).
