To outsiders the line between double opt-in and straight spam is a fine one. I have seen so many complaints from people that I KNOW are legitimate double opt-ins yet still complain. Maybe a guy signed up for a 4free site on his wife's email account and she starts getting complaints and knows she did not sign up for anything and the husband SWEARS he didn't. So a complaint is sent even though there is a remove link. Many surfers have heard that remove links are a joke and just a way for spammers to confirm that email is active so they don't bother using it. Some hate spam enough to report it to Spam Cop or an ISP if they know how to look that up.
I don't think the productivity in mailings has decreased significantly, but I do think that the amount of complaints is rising for those who do mail. Hosts and sponsors are killing accounts for those who they do not know. I have hosts and sponsors who I use that know I am mailing legit addresses I have collected myself and not outright spamming. I haven't had an account closed yet and I am pretty sure any complaints I have had were few. Keeping in contact with those who may be affected by your mailing is a good way to protect yourself. Removing people who cancel is a definate must.
Some of the free email companies are getting aggressive with dealing with spam. Some of their measures may be overkill. Hotmail is now using software called Brightmail that is supposed to be stopping spam cold. I signed up for several 4free sites last week from various 4free programs and haven't received mailings to the Hotmail account I created to track them. I created a Yahoo account at the same time and DID receive mailings to that address. Hotmail makes up a huge chunk of the addresses of people that receive mailings. That income just got cut off. I expect we will see more software being developed that will kill spam AND legitimate mailings. Of course I am sure someone will come up with a way to get around those roadblocks. If they do, drop me a line
