Haven't read what every one else has said, but both of my brothers are motorcyclists ( and I'm a cyclist, so like to think I'm more observant than most ( well, I am!)), so yes I do move over and I do notice if I'm thanked for it.
When filtering takes the piss, is , like a few weeks ago when the traffic starts moving (at traffic lights) and the motorcyclist expects me to change my pull away speed so he can sneak thru a gap between me and a big van.. This with only one other car in front and the next set of lights red. I didn't stop for him and the dick pulls up next to me when we stop. I open my window and point and laugh at him.
Anyway, apart from that, if bikes can make better progress than the rest of the traffic, I see no problem with (safe) filtering.