Spammers are evil, and persistent
How long has it been? 12 days? It took 12 days before spammers managed to circumvent my CAPTCHA by - get this - answering the question! For some reason, it is worth the time of spammers to decipher some simple human question on some low traffic blog in some far corner of the web, so they can submit some spam site in a comment on an old article.
While this revelation is both aggravating and fascinating, the CAPTCHA in general has been a success - I've gone from about 5 spam comments a day to 1 in 12 days. That's a huge win for me, and it is trivial now to modify the CAPTCHA question and stay one step ahead. Look out for the moving CAPTCHA!