My experience with forum spam is radically different ! I noticed that several of the boards that I visit are using PunBB, so I thought I'd pay a visit. I run several boards with another popular BB system. Until this year, I would have had similar opinions to those expressed about forum spam. However, this year things have changed. My boards, like many others have had constant spamming.
I encourage you to incorporate robust anti-spam measures into PunBB.
Current anti-spam measures that I have in place now on my boards - some requiring modifications:
(1) Image verification for registration - helps some, would like one that is harder to crack. Also would like the option for image verification on posts.
(2) Memberlist does not list members with 0 posts. If you have an option to sort by joined descending, you may find that spammers are in under your radar and using their website links in the memberlist to advertise porn sites, etc. We do not list members with 0 posts and plan on deleting all members without posts once a month with a script.
(3) I have never allowed Guest posts.
(4) Tried user (email), none and admin authorization - user (email) seemed to work the best in my situation - admin would be better if you know the registrants.
(5) Admin notify on all new posts (probably should also have on replies) - each new post generates an email to 3 admins - the first one to be available checks out the posts and either replies if they have something to say or deletes the post if spam - we try to be fast and get the spam off as quickly as possible. Would prefer to have an option to only notify for posts if a new or non-trusted member, but have not implemented this yet.
(6) Considering banning all registrations with .ru address, but have not done this yet.
(7) I really want an Easy De-Spam button where with one click on a post, an administrator can delete the user and all posts for the user.
With the above, we have made a definite difference in reducing spam, but I would have to say that automated and real people spammers are better at adjusting and getting on boards than I am at defending the boards. Any additional ideas greatly appreciated.
If your message board has much traffic and does not have a problem with forum spam, consider yourself lucky and I can't help wondering if you and I must be on different planets - or maybe spam is on its way.