Is There Any Reason to Report Spammers to ISPs?

marko_ramius asks: "For years I've been a good netizen and reported spam that I get to the appropriate contacts at various ISPs. In the entire time that I've done this I've gotten (maybe) 5 or 6 responses from those ISPs informing me that they have taken action against the spammer. In recent years however, I haven't gotten any responses. Are the ISP's so overwhelmed with abuse reports that they aren't able to respond to the spam reports? Do they even bother acting on said reports? Is there any real reason to report spammers?"