The Uses and Misuses of Dialect

Use of a dialect is something I am always struggling with when trying to write stories set in Detroit. Here is an article that has some good ideas about it.

http://www.justaboutwrite.com/A_Archive_Uses-Abuses-Dialect.html

How do you incorporate the kind of speech your characters use without becoming incomprehensible to your readers?

As readers, how much dialect do you want to read? Is it fair to use a little to indicate the speech patterns and then drop it?

I know it bothered me in Huck Finn, for instance.