Change the font size of text in Safari
You can change your web browsers readable text size by hitting the Command key and + key (plus key, next to delete). Changes are immediate. Continuously hitting this key combination will continue to increase the font size and you can take it to ridiculous levels if you want. Reducing the size of the browser font is just as easy, by hitting Command and – (minus key).
I use this all the time when I encounter a website with text that is far too small to be readable by any human without superpower eyesight.
This is a Safari specific tip but the key combinations generally are the same across browsers on the Mac: FireFox, Chrome, Webkit, etc.