People seem to think that spam bots are fairly stupid, but I've played the cat and mouse game with them and they've been surprisingly smart. I added an encoded cookie to the main page of the site which you needed to post but spam bots had no little trouble with that. On another site, I used simple math captcha -- but it was too simple and didn't even last a day. It seems to me that simple replacements, such as the above, would be the first thing most bots would handle.
The incentives are different between spam comment blogs and e-mail spam.
Spam primarily sells shitty stuff for unsophisticated people: if you're bright enough to obfuscate your address, even with [AT] ... [DOT], chances to sell you herbal Viagra or to phish your SSN are very low, there's little point collecting your e-mail address.
OTOH, when spammig your blog comments, the primary audiences are readers and bots, so your net-literacy isn't a disincentive to spam.
If what you do is sell a library of email addresses, it doesn't really matter if the emails are of likely "customers" or not they just need to be emails with someone at the other end.
I have 5 sites with simple math captchas and get hundreds of spam a day that don't solve the captcha and which are therefore rejected. None solve the captcha.
What do you mean by "simple math captchas"... where the distorted characters display something like "2 + 3 =" - and I'm supposed to type 5 or five?
Or are you simply using a simple math question (un-captcha'd)?
I've been experimenting with my own db of questions that can be answered with a word - including simple arithmetic and simple reasoning such as "Which is warmer? Hot or cold?" - and finding almost no spammer cares enough about my sites to develop a decoding table for comment submission [that would of course change if I were Amazon, etc.]
All of this is moot, of course, if some spammer were to care enough about auto-registering/emailing my site to get porn-visitors to solve the questions/captchas in order to "see more".
