I posted a reply here earlier today as a guest, and was confronted with an anti-spam "math problem". There was a banner announcing that my answer was incorrect (it wasn't), but my reply was posted anyway. (I didn't try it with an actually incorrect answer.)
This site is designed to take advantage of CSS. If you are seeing this, CSS must not be available or enabled in your browser. Everything should still work, but won't be as pretty. :)
Re: math problem problem
As I recall, the third-party Captcha module I use has a bug where it gives a spurious error before you even answer the question, but otherwise works fine. I'm hoping for an update to fix it sometime.
It only affects guest site visitors, and is just a cosmetic issue.