Otherwise, I think that it can be helpful in identifying issues.
We use it to help advise us with respect to the IADB accreditation database, and what we have found is that yes, there are a lot of complaints for legitimate opt-in mail, but a demonstrable change in *volume* (rather than the valid:invalid complain ratio) can often notify us very early on about a problem mailing by someone listed in IADB. Due to the nature of the senders listed in IADB, typically a "what's going on with this??" inquiry will result very quickly in a problem customer of the sender's either getting a clue or getting the boot.
Anne P. Mitchell, Esq.
Institute for Spam and Internet Public Policy
Professor of Law, Lincoln Law School of SJ