It is hard to imagine, but I have been blogging for close to seven years now, and I have seen comment spam of varying degrees. It used to be pretty easy to spot. Services like Akismet and now TypePad AntiSpam are there to help - and they do - but even trained computers fail at finding spam. Both Akismet and TPAS have been failing me lately, let me show you why:
If you read that, it is actually mostly literate English. This is one of dozens of spam comments we have been getting. They usually do not put links in the body of the comment, that is so yesterday's tactic, but do use the Author URL to link to their spam site. And some of the spam sites don't even look like spam site - they actually take a careful eye.
Spam is getting smarter. This is scary.
One solution is to use a CAPTCHA source, such as ReCAPTCHA, but these can be defeated, I have seen it happen. The drastic answer to this problem is to just turn off anonymous comments altogether, but for us, that is not an option. We want people to comment, and registration drives some people away.
The only good answer is that it takes a lot of hard work to combat comment spam, and having good policies in place help, too. See our Privacy Policy, Terms of Use, and Comments Policy. You may think that is a lot of mumbo jumbo - and it is - but it is very important for our users to know where they stand.
Such policies are required to provide a safe, engaging place for the community to not only consume, but create and share content.
Spam is getting smarter. This is scary.
One solution is to use a CAPTCHA source, such as ReCAPTCHA, but these can be defeated, I have seen it happen. The drastic answer to this problem is to just turn off anonymous comments altogether, but for us, that is not an option. We want people to comment, and registration drives some people away.
The only good answer is that it takes a lot of hard work to combat comment spam, and having good policies in place help, too. See our Privacy Policy, Terms of Use, and Comments Policy. You may think that is a lot of mumbo jumbo - and it is - but it is very important for our users to know where they stand.
Such policies are required to provide a safe, engaging place for the community to not only consume, but create and share content.
Anonymous comments are always moderated, please sign in and join the discussion. 
I'm having the same problem and you nailed it. Perfectly literate but completely nonsensical. I was a bit slow to delele it at first, but that just encourages them.
Is there a way to band-aid the problem by turning the Author URL's box off by default that you know of?