Everyone has been very supportive in helping me deal with the comment spam issue. Thanks everyone.
I thought my troubles were over when I got two comments just now with "interesting..." and "page-rank?" on my last two post. The links were to a casino site. These comments were probably not machine scripted like the other comment spam, but they added no value to the comments and the casino site URL made me feel that they had posted the comments for the purpose of trying to steal page rank on Google. I have a feeling some bloggers also post comments on my blog just to get links to their sites.
My current policy on this issue is, if you post something on my blog that clearly adds no value to the conversation and if your URL is a gambling site, a porn site, a pharmaceutical site or some other obviously spam friendly commerce site, I will delete the post and add you to the blacklist. I will discourage bloggers to post opinion-less or off-topic posts just to get links. I continue to encourage people to post their opinions whether they are supportive or critical and of course I will not delete critical comments.
My policy may change, but this is it for now.