How can I force pinch-to-zoom on some websites?
Ugh, this is so annoying -- it is the height of designer/developer arrogance (in my opinion -- and I'm a developer myself). The other answer's code did not work for me, but after much experimenting I got this to work (iPad 3/iOS 5):

javascript:document.querySelector('meta[name=viewport]').setAttribute('content','width=device-width,initial-scale=1.0,maximum-scale=10.0,user-scalable=1');


Use the same method as the other answer says to add it (create a bookmark for any page, then edit the bookmark and replace its URL with the above code).