The more I hear about blogger and cartoonist Barry Deutsch's sale of his URL amptoons.com to a Search Engine Optimization company, the more I think, "What was he thinking?" If you build up a good reputation for a URL such that it's worth something to a SEO, then when you let a SEO start loading it up with spam and other questionable types of links you are officially extracting that value. Like oil from the ground, that URL is going to go dry and won't be worth anything at all after a period of time.
The shame is that Barry didn't seem to realize that his sale of his URL meant that he was no longer building the value of that URL (it also appears he may be getting screwed on the terms of the contract – see very bottom of the above linked post). For after all what is the value of a URL? Some specific stuff like pagerank at Google, trademark-like recognition, but also the associated content and community of visitors to it. All of that is seriously compromised: the pagerank tanks, the trade-mark aspect gets tarnished by association, and the community, at least in this case, got seriously upset.