This is what I got in my inbox a few minutes ago:

Hi,
We found the following 9 broken links on arnab.org:

On page http://arnab.org/blog: 
http://arnab.org/properties.php : Not Found
http://arnab.org/blog.php : Not Found
On page http://arnab.org/blog/: 
http://arnab.org/blog/properties.php : Not Found
http://arnab.org/blog/blog.php : Not Found
...

For just $5 (US) per month we will check your website regularly, and warn you of any future broken links. Your website's visitors will thank you for it. [direct paypal link]

The broken links he sent were correct - so the email was pretty helpful, and I would consider it if it was a little cheaper. That's what I call good marketing.