MAN! I forgot all about that... ahahaha!
Dart wrangling was soo much fun... haha. It was actually better then grapple monkey if you knew how to structure the correct bind, just press a button and YEEHAW! The arc that the darts made allowed you to move in both plains at the same time, making you a difficult target to hit.
I can remember going "Offensive" (note the pun) Engineer on a public server and ganking the flag. Dart wrangling across mid, Pub snipers just werent good enough to take me out. I think there was an outcry on the forums that week ;)
That and the FOV from my end felt like you were riding a bronco. Too much fun. Its probably better to be left out though, it was grappling without a wall, kind of like a jetpack for the engi.
shoot now I am getting all misty eyed again.