I was writing an email early this morning and made a mistake.  In the middle of typing a word I accidentally struck the Command+. keys (Apple+Period).  To my surprise, Apple Mail displayed a drop down list of possible completions for the word I had half entered.

At first I thought the feature was a novel idea.  But the more I considered it, the more I gained a genuine respect for what the feature represented.  For someone in some way keyboard challenged, this could represent a very efficient way to enter text (at least the larger and more complicated words).  For someone spelling impaired, the feature could be a powerful way to reference possible spellings without waiting for the spellcheck to call their bluff.