The Pesky Typo Hunt explains how these small errors can sabotage your manuscipt, and the best technique I know to hunt them down and destroy them.
A Point of E-tiquette discusses--in language so plain and simple as to command even a teen's respect--why you need to run the spellchecker!
In Bage and Handcuffs, I talk about why things like typos, and spell checking, and grammer that works, really do matter--even if your reader may not be conscious of them.
Many writers will at some point want a pro to read their manuscript--Pitching to the Pros discusses whether you should try this, and what you can--and can't--get from it.
And The Editor is Never Wrong, Mostly deals with the question of how to respond when you disagree with editorial suggestions.