One big headache for everyone that have a website today is how to make the communication with you readers as painless as possible and still be able to block spam.
I have to come back to WordPress on this and their plugin - Akismet.
For several years now, I have been running a WordPress blog with Akismet enabled. And it just works! With this, I do not need any Captcha. And my users are happy because there is no need for any additional steps when posting comments.
I do have a policy where I que all new commenters and also que them if there are any links so that I have to do some manual approval. But Akismet really cuts down on the work I have to do.
I wish K2 would add Akismet support for commenting. It would make our days as admins a lot easier, and that is what this is all bout, right? :-)