It is pretty bad in many respects. For example, it seems to ignore the "display" attribute, so "display: block" and especially "display: none" don't have an effect; as a consequence, every external link has their URL next to it, which is pretty bad *especially* on a small-screen device. :-(
Actually, I think hiding things using CSS is probably a rather bad idea anyway - I know it's kind of cool that it's possible, and it's certainly an elegant solution where available, but invisibility is one attribute that really doesn't 'degrade elegantly' if unavailable.
I was thinking of pointing this out somewhere before, if it hasn't been already, since text-based browsers (for instance) have the same problem. It looks especially ugly for footnote-style links ("[1]" et al) and links typed in the form "[http://example.com http://example.com]" - although the latter are broken at the moment anyway. :-/
I'm not sure what a better solution would be, but maybe some JavaScript voodoo to add them or uncomment them. In general, I dislike relying on JavaScript even more than I dislike relying on CSS, but I accept that this option is never going to be viable server-side, and presumably people wanted it.