Watch Out for Mistakes Missed on Porpoise...
The Problem:
The spelling checker doesn't alert you to the possibility that a word may be the wrong word, even though it's spelled correctly. Purpose or porpoise? Mourning or morning? These mistakes make me look real dumb.
The Solution:
You said it. The spelling checker actually does catch a few correctly spelled problems of word choice and grammarfor example, it'll suggest "must have" instead of "must of" and "there are" instead of "their are," because these examples are always wrong. But beyond that, the spelling checker can't help you if you've got the wrong word. This is a job for a dictionary, a helpful colleague or friend, or a professional editor.
Tip: If you don't have a dictionary on hand, check out Merriam-Webster Online (http://www.m-w.com).