In an earlier discussion about commenting Kris mentioned using pingback, but...
Spam is a problematic issue. I had to enable comment moderation not because the Captcha was too easy to come by, but because apparently real people are adding genuine comments and are actively abusing the URL field to point to their commercial (or virus-infected) websites.
These comments are looking pretty normal, thanking me in person for a specific article about a subject or even pointing out an issue. Hardly the work of an automated process. These people are either being paid or directly profit from commenting on blogs.
After enabling comment moderation the number of spam averaged to 3 to 4 a day. Moderation helps me not to go and look for these comments and prevents harm to innocent visitors, but unfortunately diminishes real interaction between readers (and me).
Pingbacks are actually a much easier way to distribute spam with less effort and for that reason alone I have no intention to enable it (or even use it moderated). I am too busy with moderating my comments, thank you :-)
After consideration and discussing with others having identical feelings, I concluded that it was not just the fact that one is commenting on someone else's blog article, but also the manner (addressing, self-promotion and confrontation). I realise that this is more a style-related discussion and more based on perspective and personal likings than merely the burden of having comments linked unidirectional.
De gustibus et coloribus non disputandum est.