Do you guys usually quote OP when reaponding to a thread? Seems a bit redundant to me honestly
I basically never make a post without quoting somebody. The only time I don't post a reply to somebody is if I'm posting an image in a thread about dumping your X folder or something like that, or if I'm changing the subject.
If I'm speaking directly to OP (to answer a question) yes.
If it just a post to share views, no.
How to tell when 4chan is being invaded by outsiders:
They question basic site functions.
If I read through a thread and there's some long tangent going on, I usually then quote the OP if I intend to respond to him, in some way that hasn't already been done. I make sure not to be redundant, of course. It makes it easier for the later readers of the thread to pick out a response to the OP: it's for their convenience. I'm simply being generous and thoughtful.
I just like clicking on the quote link. I change it multiple times though when responding to a thread and or poster so that I don't get accused of being a samefag (the worst thing you could call someone, a person involved in a discussion)
When the thread gets big enough, it helps the OP (and others who are interest) easily find replies that are directly to their post. It's not the worst idea if you want them to see something you said.
I do if there is a cute Saya pic as the OP.
Otherwise usually no if the thread is off and going and the OP was not specifically asking something I felt compelled to reply to. Not sure where I draw the line but it isn't very far, probably 50+ posts in I ignore the OP unless for some reason everyone is starting with him.