John-Michael Bond, writing for The Unofficial Apple Weblog:
Let’s say that I forgot to capitalize the word “church” in the text below, and want to do that after the fact. To do this, I simply select the word in question by tapping it twice, tap the shift key, and select the proper spelling from the predictive typing menu.
Now say you want to make a word all upper case letters. Here, you simply tap shift twice once you’ve highlighted the word — effectively activating the caps lock — and predictive text offers up a number of fully-capitalized suggestions as a replacement.
A fantastic tip that saves both time and frustration compared to the traditional method of placing the cursor prior to making an edit.