A HighRankings Forum thread named The Dangers Of Link Requests, When You're Not Very Careful, discusses some of the risks involved with link exchange requests.
We all get them all the time, I actually reply with an auto-responder (if certain criteria are met) with some automated link building tips (not like they read them anyway). But what do others do with these requests? Many delete them and forget about them but most get caught by spam filters. Other's post the request publicly for others to mock and make fun of. Some registrars hold you hostage demanding you pay $200 per domain name for the unauthorized mass emailing of these link requests.