If you do these things successfully, your letter will be short, hard-hitting, and memorable. It will add insight beyond what the reader would obtain from your resume alone. It will not be generic-that is, another candidate writing to the company would not be able to say the same things you said in your letter. Your situation should be unique to your experience. Always write to an individual by name.
First names are usually the preference in the United States.
In addition, I have owned two Audis, and am a fan for life. I am hoping you can help me get my resume circulating among the various plant managers who might need an MBA intern this summer. Try to start with a reference the reader will know. For example, if someone referred you to the person, start by referencing that connection. Note that it is likely the same letter will not work for any two companies you write to, although it can work for different people within the same company.