Other than acting as an introduction to your resume and to tell the employer what position you are applying for, what’s the purpose of a Cover Letter?

In the 9/3 New York Times, Jason Fried, , Chief Executive of Basecamp, a privately held web application company based in Chicago, gives us an inside look at their hiring practices. “We focus initially on the cover letter, and if you just email us a resume, you’re out.”

Besides being very well written and short, what should the cover letter cover?

-Who you are and what you do
-The job you are interested in and why you want it
-How you believe you can fill the employer’s needs