There is nothing worse than getting automatically redirected to a mobile version of a site, and not having (or not easily finding) a "view normal site" link. It's not just that the mobile site is a scaled down version of the normal site, it's the unfamiliarity - the sudden 1-dimensionality of what used to be a 2-dimensional page and the obscene amount of scrolling required. The previous mental map of the site is no longer accurate.
On the Boston Globe site (the oft-cited shining example of responsive design), I find the amount of scrolling to be extremely painful if I am not looking to read in a linear fashion. With the retina display on an iPhone, the desktop version would be discernible and immediately navigable with a quick tap-zoom to any location of the page. As with most responsive designs, the "view normal site" option is not available.
Should users be forced into a responsive design? Should they be able to toggle if off to "view normal site"?
Below are the estimated viewport overlays of an iPhone on the Boston Globe site at each view:
=== Update 2012-09-12 ===
Some prototypes have emerged recently: