Edit: 2013-05-23. Removing the links to Twitter, those are 404 now.
Today I've got this message from @unixthis. He has a good point there, and it is really time consuming to deal with comment spam, time that I can use to write more how-tos or info you may need. But it is also true that a blogger needs feedback and it should be easy for the readers to give that feedback.
Giving this fact, the problem is still there, should a blog have comments off or on?
Maybe a good option is something in between, turn the comments on for some days after the post is published, and turn them off later, this way the readers of the blog, may comment on it, and create a discussion. Once the post is cold, and the comments sections is off, a newer reader can still use other ways of contact to ask for support or to express an opinion about the article.
I'll try this way for some weeks and see how it works.