started to realize that for me it's never about someone falling bhind on responding to a popular story or even not responding at all...we all get overwhelmed or just can't catch up or have RL issues interfere...it's the systematic no-reply policy or (almost worse) the selective policy (i'll only respond to my friends).

Yeah, that's pretty much exactly where the line starts to get drawn for me. As I said in comments to little_murmurs and telesilla I don't keep a list of people I've feedbacked and check off whether I recieve a response from them or not. But if I leave someone feedback often enough and never hear a word from them, chances are I'll start noticing the pattern and without anything else to go by, I'm pretty much left to assume that they're not interested in encouraging reader response. However, if I know why a particular author doesn't respond to feedback, I'm probably going to be a lot more interested in continuing to leave it for them. Where I draw the line is when I see an author continue and continue to ignore feedback without any sort of response at all. That has always felt more like a closed door than anything else. Even worse (to me) is seeing an author pick and choose whose feedback they'll answer and noticing that it's only their friends that they reply to.