Phil Ringnalda started a big debate about how O'Reilly is causing link spam. One example he gives, and there are many more.
O'Reilly's ONLamp.com site, home of tons of interesting articles on Linux/Apache/MySQL/Perl/Python/PHP over the years, now also features (at the bottom of the left-hand sidebar, under the "oh, but it's related, really" headline "Travelling to a tech show?") eight links to the sort of garbage hotel sites that make it utterly impossible to find any useful information about hotels on Google.
Now this caused a response by Tim O'Reilly, where he asks, is it Search Engine Spam? Oh boy, did that get some responses. After reading through his detailed entry, you get into the comments area, where you have well known writers, industry leaders and Matt Cutts (from Google) getting into the debate. Ultimately, the bottom line is what Matt decides and this is his comment:
As others have noted, if you're going to sell text links that pass reputation/PageRank, the way to do it is to add rel=nofollow to those links.
Tim points out that these these links have been sold for over two years. That's true. I've known about these O'Reilly links since at least 9/3/2003, and parts of perl.com, xml.com, etc. have not been trusted in terms of linkage for months and months. Remember that just because a site shows up for a "link:" command on Google does not mean that it passes PageRank, reputation, or anchortext.
Google's view on this is quite close to Phil Ringnalda's. Selling links muddies the quality of the web and makes it harder for many search engines (not just Google) to return relevant results. The rel=nofollow attribute is the correct answer: any site can sell links, but a search engine will be able to tell that the source site is not vouching for the destination page.
There is a forum thread about this debate at Search Engine Watch Forums under the title; O'Reilly In Off-Topic Link Selling Debate.