From my experience with Sblam! filter there's a lot of technically incompetent spammers, who nevertheless keep trying, probably because there's a lot of unprotected mails to harvest (and unprotected sites to spam), so even simple obfuscation might stop some harvesters.

OTOH updating regular expression in a harvester to look for (@| AT ) is not rocket science and probably some spammers did it already.

Anyway, I think that puzzles that annoy humans are not worth it. I've devised standards-compliant obfuscation that encodes mails with entities, urlencoding and adds untypical constructs to the URL and HTML:

http://hcard.geekhood.net/encode/[email protected]

This gives link that is readable and fully functional for real users, but can be harvested only by spammers who take effort to parse HTML and URL correctly (it might avoid some spam, or at least it promotes web standards among harvester writers! ;)

From my experience with the Sblam! anti-spam service there's a lot of technically incompetent spammers, who nevertheless keep trying, probably because there's a lot of unprotected emails to harvest (and unprotected sites to spam), so even simple obfuscation might stop some harvesters.

OTOH updating regular expression in a harvester to look for (@| AT ) is not rocket science and probably many spammers have done it already.

Puzzles that annoy humans are not worth it. I've devised a standards-compliant obfuscation that encodes mails with entities, urlencoding and adds unusual constructs to the URL and HTML (source code):

http://hcard.geekhood.net/encode/[email protected]

This gives a link that is readable and fully functional for real users, but can be harvested only by spammers who take effort to parse HTML and URL correctly (it might avoid some spam, or at least it promotes web standards among harvester writers! ;)