A Search Engine Watch Forums post has the first documented, public, case, that I have seen of someone receiving an email from the Live (MSN) Search team for being banned for using link exchanges. Here is the email as reported in the forums:
Your site is acquiring links through posting to or exchanging links with sites unrelated to your site content. Techniques which attempt to acquire unrelated spam links in order to increase ranking are considered spam and your site has been excluded from our index as results. Please contact us once you've removed these links and we will reevaluate.Live Search
So, Microsoft is making an effort on spam. But I believe, not 100% sure, the way Google handles unrelated links to your site, is by not banning your site, but not counting those links. Unless, of course, it is a clear and transparent attempt for you to hurt the search results.
Of course, I do believe Google applies the Minus 30 penalty to some sites participating in some link exchanges or communities that are outright done for the purpose of ranking well.
Forum discussion at Search Engine Watch Forums.
