I was getting hit by comment spammers in the last week who were using URL-encoding of their addresses to get around the comment blacklisting filter I use. By replacing regular characters with the multi-character encoded representation of those characters within the URL the spammers were able to post comment spam with links to casino and porn websites to my blog.
This type of spam is a reversal of the same method for hiding your own email address in a web page so it won't be harvested by email spammers (see for example Chip Rosenthal's Blog entry).
I just added a regular expressions in my blacklist file to block the use of URL encoded characters in all links. If your blog comment software supports this approach you might want to do the same thing.