There are two routes to go: a donation button or a subscription button. I chose the latter, because at least there were additional benefits in return. Also, there are minimum transaction fees that eat into the revenue with lots of small payments. The additional accounting time further makes them less worthwhile.
Also, do remember that its not just about hosting costs, plugin costs or software licenses. There is a lot of time that goes into keeping the site going, fixing things, promoting it and more. You don't see this stuff but there is a lot of it. For example, its week 3 now and we still haven't worked out why we need 4 CPU's to run this site now rather than the 1 we had before. No one pays me for those 3 solid weeks of work on this one issue.
Bob, I appreciate your comments. If I was just trying to milk all the visitors, I would have implemented a donation system years ago when it was suggested. Instead, I wanted to give something in return, considerable time researching what the options were and how to implement them, doing all the coding myself. To my mind, removing ads in the most prominent locations was a priority for paying members. We get loads of people who lurk and bounce of the site. Some of those leave via ads. However, we also have lots of regular members who ask questions or help out others. To my mind, if they donated I would like to get the ads out of the way to improve their user experience.
pwbrown, I am not saying I am right and you are wrong. Instead, please consider that I have to chose one of two main options for forums and also that running forums is a fulltime job.