Comments are Garbled Text

Those sorts of comments are in fact spam. Some are inserted by scripts (some of which are in fact buggy) and some manually. Some of what is going on is testing to see if the spammer can in fact post random junk to your site and some of what is happening is the spammer checking to see what sort of meta characters work. The use of square brackets is an attempt to see if your blog comment entry form accepts a certian sort of markup (WordPress doesn’t, but other blogs, wikis and formum systems do.)

You should just spam these posts. You might want to consider some sort of human testing plugins and/or spam detection plugins to deal with this.