EGOL pointed me to Russ Jones' (of Virante - new to me, but they've supposedly been around since 1998) new blog, where he's writing on the topic of consensual relationships (I know; it sounds like the title of an "after-school" special, but it's quite good):

Search engines have long chosen to believe that, by default, all sites are to be included in its results. This opt-out method is simply not consistent with the consensual model. If Google will not take the time to read the TOS of various sites or, at least, use an opt-in method for its cache and index, it is automatically excluded from this model.

Simply put: You are not responsible for what Google takes from you. Period. You may want to respect it if you wish to protect your site rankings, but you are not ethically, morally, legally or otherwise obligated to it within a consensual model of ethics.

This is a breath of fresh air for most search engine optimizers who find it hard to beleive that they are called unethical for placing a reciprocal link or using CSS to place text at the bottom of the page which occurs at the top of the code. Do not get too hasty with your comment spam tools, though.

If this sounds like old material we've all heard before, give Russ a chance. He makes some very good points, and speaks from a perspective that sounds remarkably like a professor of ethics.

p.s. I'd like to point out that Russ went about being "found" by SEOmoz in a very clever way that illustrates the value of blog comments. I noted that earlier today, he left comments in two posts on the site, where EGOL clicked on his username and found his profile (note to members - update your profiles!) and website. When EGOL found the entry interesting, he pointed it my way. For all you link builders who think commenting on blogs is just spam, think again - a smart comment can mean a clickthrough from your exact target.