The iPhone's custom auto-correct dictionary (located at /private/var/mobile/Library/Keyboard/dynamic-text.dat for all your jailbreaking, SFTP-ing types) doesn't update itself when you're using, say, Notes. Using Mobile Safari's Google search box, however, seems to instantly refresh the file.
At the same time, Notes and other type-friendly apps will pick up whatever additions you make with Mobile Safari." Via lifehacker .