Not really. Most enemies approach the horse too quickly to make use of the option, and having to move away, take aim, and fire before they close in just hasn't been worth the effort.
Then there's the issue of the camera swapping angles when changing out weapons/arrows.
For giggles, I tried fighting a dragon on horseback last night.
When you get the patch, try it.
Then you'll understand.
By the way, have you seen a horse head around here? Mine's gone.