Whatever you do when you set up your blog or website you must be diligent in pulling the weeds in your site, which is SPAM. Yes, people leave these asinine comments which usually have NOTHING to do with your post, but it includes a link to their Adsense site, which consists of two links and a thousand AdSense ads. I spent yesterday cleaning out a whole bunch.
John Chow has been running a good segment on the importance of using WordPress to clean out the comments and to set up your comment PHP utility so it is not easily attacked. In Blogspot, it is a lot harder to do BULK removal of crap comments, so I have to do it 1 by 1, and each 1 gets me more and more frustrated.
I wonder if folks make money on this kind of stuff? They must, given the proliferation of these crappy comments on my site at least.
Remember to install an Anti-Spam plug-in like Akismet or the like and much of this crap goes away. If you are using Google hosting, their algorithms work well as well.