Google's Auto-Link adds links to certain kinds of content that appears on web pages (like a link to Google Maps for addresses, or Amazon for ISBNs).
Some people (like Dan Gillmor) are viewing this with suspicion. (The Trademark Blog has collected the commentary.) They shouldn't. The issue is simple: Who owns your desktop? You, or the owner of whatever webpage you happen to be browsing?
A meatspace analogy should make this clear: Imagine I have a butler whom I task with going through what drops into my mail slot each morning. His job? To annotate my snail mail. He goes through the advertising circulars and researches whether better prices are available anywhere else. He gets me a map of every return address. Maybe I ask him to anticipate needs I don't even know I have yet. If he does something I don't like, I replace him.
When I visit your website, and you send me a page in response, I should be able to do whatever I like to manipulate it on my end. Display it in purple, suppress images, block pop-ups, compare prices from other vendors, whatever. In the words of my colleague, Cory Doctorow, "it's my screen, and I should be able to control it; companies like Google and individuals should be able to provide tools and services to let me control it."
Of course, we have to make sure the butler doesn't try to take over and act like a jail warden (i.e., monopolists forcing you to take a butler). And we don't want the butler to sneak into your house when you're not looking (i.e., spyware). But Google's Toolbar seems to be a pretty good butler -- it's not like he hides his presence, and you can fire him anytime you like (it's not as though Google's leading position in search gives it much ability to force its butler on you; you can choose from lots of other "toolbar" apps that can submit searchs to Google).
So I say mark up my webpages for me, butlers of the world, make my web more useful!