Is there any reason to report spammers to ISP's?

marko_ramius writes: For years I've been a good netizen and reported spam that I get to the appropriate contacts at ISP's. In the entire time that I've done this I've gotten (maybe) 5 or 6 responses from those ISP's 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 to respond to ANYBODY that reports spam? Do they even bother acting on the reports?

Is there any real reason to report spammers?