Mark Nottingham has a good set of background links on why being able to GET web resources is a good thing - prefetching as a means to performance - mnot’s Web log: Prefetching (again)
His article is partially in response to recently publicized problems that a Web application had when Google's "Web Accelerator" retrieved pages from links within a page - the application had used those links to perform a 'method=delete' operation. This causes peoples data to disappear silently, because it was pre-fetched.
This issue has been raised time and again, and unfortunately web designers continue to learn the hard way. I think the biggest idea that a Web designer should take away from this is that "a link is not a widget". Within a Web page (or music playlist, or RSS feed, or SVG drawing, etc), links to be clicked on are simply not to be dressed up as if they were buttons - a link is not a widget.