It's fantastic if you sneak up behind people, pretty much instant death, need to be a pretty awesome flanker though. I prefer the airblast, it's handy when your medic's on fire, or if you want to stop a Scout from escaping and of course reflect kills against demomen, soldiers, stun balls (IMPRESSIVE), lv3 sentries (UNSTOPPABLE) and snipers using the huntsman (GODLIKE)
Wait, you can reflect the rockets of a level 3 sentry? I tried numerous times and could never do it.
And I guess it would be obvious you could reflect an arrow..