If you are concerned about linking to a possibly “bad neighborhood” that has relevant and helpful content for your site users, there are solutions.  You can of course use the nofollow tag (which Captain Sprite is a big fan of).  However there is some evidence that the engines are still following these links. 

What is a paranoid webmaster to do?

Make it too hard for the search engine robots to follow your link.  You can do this by using javascript or redirecting the user through a directory that is blocked with your robots.txt.  Thus placing the link out of the current reach of the engines.  This way you can link to anywhere on the Internet and not have to worry about triggering an penalty for linking to bad places.  That is at least until you get a hand review.  But hey you were only linking to good content that just happened to be in a bad neighborhood. Right?

p.s. be careful that your redirect solution is not exploited by others (in other words keep an eye on your log file for weird referrals hint hint)