I'm a QF proponent for sure. I think it's going to freshen up the game, and there will be some teams who run it almost exclusively, but for the majority of people it'll be used a little less than kritz is, to throw a different look at teams. It'll be my medigun of choice if my team wipes at mid, for sure. It's still really easy to focus down targets who are QF'ed. Teams seem to be treating QF ubers like they're kritzes, where you focus the damage dealer first. It's really easy to kill a QF'ed medic with focus fire and traps, and after the medic is dead, you're left with a half-buffed soldier/scout/demo to contend with. QF is incredibly easy to counter as long as you know it's coming. If you can't scout out the uber that the other team is on properly, then that's a skill you need to learn. It's kinda hard to miss a QF medic though, he's usually flying through the air or running alongside his scouts.
All that said, it's really silly that it was allowed this season. It's going to put a tint on playoffs/LAN, as right now the QF clearly favors the team with better DM, as others in the thread have said. I would have much preferred an offseason to work all of this out and see the QF used to its actual potential rather than just as an excuse to turn every push/hold into a messy DM-fest.