For example, here is a sample comment:
The text appears to have come from an article titled Basic Writing 1000 (Google search to find it). This comment was posted on goulo's entry which happens to be about word usage. There must be some kind of matching algorithm going on to pick relevant text to post in a comment.
You will probably notice this sort of activity in your journal, if LJ doesn't implement some technical measure to stop it. The spambots are getting smarter, they are learning how to post to your journal with real-looking accounts. I don't have any clue what the ultimate goal for them is, unless it's just to practice making a smart bot to be used later for spamming.
I have anonymous comments on my journal screened automatically so I have to manually approve them. Up until today, most of the anonymous comments have been spam. If this keeps up, I will probably upgrade my default settings so comments from all non-friends are screened until I approve them. It's a sad state of affairs but at least some tools exist.
One thing I would like is the ability to close comments for a post. I have 454 past entries, all of which are potentially open for random drive-by spamming. If anybody from LJ happens to be listening (ha ha), please add a "closed to new comments" flag!