The problem of spam has now got silly and there are many people doing many things to reduce it. Personally I use some simple javascript on my contact page to generat my email address on the browser to prevent it from being harvested, and that works rather will, although I would never put my personal email address on a web site. I have also been playing with BoxBe that requires users to interact to sent the mail to me. That is also working well, but it appears many users can not be bothering to follow the process through and email is not getting to me.
Following a discussion with a friend I started using Project Honeypot to try and trap these harvesting spam bots by feeling varying email addresses to each IP address visiting our sites and then seeing which of these addresses get spam sent to them. This has also worked well, but other than seeing the breakdowns of where the spam is coming form it has been of no use until now. Currently Project Honeypot are releasing an announcement every day this week and today http:bl was announced. This is a similar service to email DNS block lists but lists the servers that look for email addresses and not the ones sending the spam email.
I have produced some demonstration PHP that will make it easy for most people to contact me normally (still using the javascript), but make it harder (probably using BoxBe) for people and bots coming from suspect IP addresses. Click for my http:bl example code.
Update: Yes it will work if you are using OpenDNS. This is why I check the first address octet is 127.
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After my request, OpenDNS have marked the httpbl-server as DNSBL-servers which means there will be a proper NXDOMAIN reply. This also means the 127-check is not strictly needed for correct behaviour with OpenDNS.
I just use a Java applet form on my site with some plane English for those that don’t have Java installed.