Over on Tom Peters Blog, he posts about people speaking and writing in a way they can't understand themselves.
This is one of the first things I did when I started my current job last year. The staff seemed to take on another body when they had to write a letter of email. They suddenly use words they'd never used before and didn't understand. Even worse the customers didn't understand either.
The letters and emails looked like a dictionary had been emptied on the screen.
The best advice I've ever had was from Courtney Ferguson a great DM copy writer (I wish she had a blog). Her advice was write how you speak, be personal, engage, do something unexpected. Her copy is joy to read and the best bit is it sells too. You don't notice it though. That's the best bit.
I pass this on to anyone who'll listen. Please do the same.