Straight from the horse's mouth: "Don't participate in link schemes designed to increase your site's ranking or PageRank. In particular, avoid links to web spammers or 'bad neighborhoods' on the web as your own ranking may be affected adversely by those links" (http://www.google.com/webmasters/guidelines.html). And from Google Hacks: "When you receive requests for links, check sites out before linking back to them. Check them through Google for their PageRank value. Look for directory listings. Don't link back to junk just because they asked you to. Make sure it is a site similar to yours and on topic. Linking to 'bad neighborhoods,' as Google calls them, can actually cost you PageRank points" (302). And to reiterate: "Bad neighborhoods are those sites that exist only to propagate links. Because link popularity is one aspect of how Google determines PageRank, some sites have set up 'link famrs'---sites that exist only for the purpose of building site popularity with bunches of links. The links are not topical, like a speciality subject index, and they're not well-reviewed, like Yahoo!; they're just a pile of links. Another example of a 'bad neighborhood' is a general FFA page. FFA stands for 'free for fall'; it's a page where anyonce can add their link. Linking to pages like that is grounds for a penalty from Google. Now what happens if a page like that links to *you*? Will Google penalize your page? No. Google accepts that you have no control over who links to your site" (306). I'd pay attention to that last little paragraph, as it helps to address the other side of the issue. Needless to say, if a high PageRank and a good listing in Google is a high priority of yours, I'd be wary of just link exchanging schemes, especially ones where the site in question doesn't have a similar topic to your own.