I've seen a lot of movies where all of the dialog was voiced over from the studio. I'm beginning to think that most of them might be this way.
It's called ADR (Additional Dialog Recording), much of the dialog is still recorded live, but if there's anything that's not clear, or a line that needs to be changed they'll pick it up in post ADR.
I hate ADR'd dialog, so often I can tell which lines were picked up. It'd especially obvious when there's a 1 on 1 conversation that usually shows the person's face who is speaking, but for some lines the back of their head is shown instead. That line has likely been "looped".
The other thing that bugs me is noise gating dialog. Yeah, I understand that sometimes there's something making noise on set that wasn't noticed, yet the take was otherwise perfect. But keep the background noise constant, don't make it go silent between each line, that's just draws attention to the noise. (See CSI this season in the interrogation room).
