On my iPhone 4S running iOS 5.1.1, the "add comments" link is completely broken on mobile Stack Overflow only. Desktop Stack Overflow and Meta work fine (as does, I assume, the rest of SE's sites). I have over 7,000 rep and am not on any kind of ban or probation, so I know that's not an issue. Ack, it's just so annoying to use desktop view on an iPhone!
UPDATE: It appears now to be limited to questions that I myself have asked on SO.
UPDATE 2: The iOS 6 beta 1 version of safari has completely disabled the commenting link and the notifications drop down in both mobile and desktop.