My philosophy with reading for feedback is pretty much my philosophy on lending things...I won't unless I'm ok with the fact that I might not get the feedback I'm expecting back...
I don't really feel comfortable harassing people beyond a polite reminder that there reading has been posted so its more...if you don't give me feedback fine, we're cool, ill just be highly disinclined from reading for you in the future. Like with the lending. I wont cause drama if I dont get something back. If it really meant a lot, I wouldn't have let you borrow it. We'll be fine, I'll just never lend you anything again :0
It is rather inconsiderate, though. Even if you're busy...if you know thats the case, dont ask for a reading where feedback is required. And if something comes up...well, late feedback, with an explanation, is much better than never...