Here's some advice for people writing cover letters. Don't take any of the standard career-services-office advice for writing cover letters, or your cover letter will look exactly like everyone else's cover letter. If you write one of those “I work great on teams but am also a strong independent worker” cover letters, your cover letter will look just like everyone else's, and you won't stand out. The way to stand out is to write a letter that reflects your unique personality and highlights the reasons why you want to work at the place to which you are applying. 95% of the cover letters I receive do not include anything about Fog Creek and show no sign that they have been customized in any way for the job in question. This sends a signal that you are simply spamming your resume to hundreds of jobs, which, in turn, sends a signal that you are both desperate and not willing to work very hard.
Here's the thing: the very best candidates have come to realize that they have a choice of where to work, and when they apply for a job, they are applying because there's something intriguing about that particular job, not because they'll take any work that comes along. And you can see it in their cover letters. For example, if I were to see something like “I'm happy where I am, but I've always wanted to move to New York and if Fog Creek is anything like you describe it on your website, it sounds like a great place” you would sound a lot more desirable than someone who writes, “You will find that I am a very hard worker.” If you make your cover letter interesting, make it personal, and drop hints that you have choices in the world, you will sound more like one of the top 1% candidates.
By the way, we received something like eighty applications for our opening. Probably 50% of those people were qualified and at least ten of them were great. I won't say more because we're still in the interviewing stage. [Joel on Software]