A few weeks ago I made a bookmarklet for iOS that re-enables zooming and also sets the viewport width to the device-width (this is useful for pages that use the whole width, which leads to small fonts. E.g. Hacker News).

It works quite well.

javascript:(function()%20%7Bvar%20meta%20=%20document.createElement(%22meta%22);%20meta.name%20=%20%22viewport%22; meta.content%20=%20%22width=device-width,user-scalable=yes,maximum-scale=10%22;%20document.head.appendChild(meta);%7D)()