Sometimes, you make a mistake in typing deliberately or non-deliberately, and your subscribers get to one of your recommended websites and you make a sales... Have you tried that before? I have, a couple of times, and it works as long as the recommendations are relevant I guess =)
Example: I use ViralURL to cloak my links, and I type in the wrong keyword... http://viralurl.com/recommending/wrongkeywordtyped (Try clicking on the link a few times and you'll see a different site appearing each time...)
Sometimes, the person who's looking at your site types in the url wrongly... should be ending up with an error page...I configure the error pages to what I'd like people to see, and kaching!
Example: User types in http://HomelySuccess.com/wrongredirectword
Hope this little tip helps!