Effective communication skills, especially the written kind, are a must for today's workplace. This article explains it well. I don't care if you were a math major and never had to pen a term paper, you should learn to compose your thoughts in a professional, concise, and (preferably) error-free manner.
The current economy only ratchets up the pressure. If you're searching for a job, any grammar mistake on your resume or cover letter is the equivalent of a gymnast falling off the balance beam. You've differentiated yourself by your mistakes.
Don't be that gymnast. Read whatever you've typed before you hit the "send" button.