I used to work in a word processing department for a medium-sized law firm in Washington state. Personnel in our department were responsible for proofreading their own documents. This is frequently a good way to miss typos, as your brain knows what you intended to type and skips over misspellings.

One of our lawyers filed the paperwork in Olympia for a "pubicly held corporation." The documents had been read by at least three people: the word processor, the filing lawyer's secretary, and the lawyer himself. All of us missed it...

Lin