Just installed the recaptcha on this blog, hopefully will remove all the comment spam I have been getting lately.
reCAPTCHA is a great concept, they scan in text from old books and then use human brain power to digitise the text by solving captchas. So not only are you fighting spam on your blog but you are also helping to archive and digitise more of humankind's knowledge. Cool eh?
If anyone is interested I can put up some instructions on how to implement this using Django's Free Comments.