I know I've talked a lot about job hunting...blame the economy.
Recently, I posted a job ad for a part-time job helping me out on some personal projects. In it, I asked applicants, as a bonus to list three websites they like and one or two sentences on why. This proved to be a great idea. I was easily able to sort out "nos" and "maybes" by who did the bonus and who did not. When people just replied with a form letter & resume they were a "no". It seemed like this was one of a dozen or so of jobs to which they were half-heatedly applying in that session.
Some applicants took it a step further and mentioned why they were looking for work. I think this is obvious but I'll say it anyway, If you are looking because you need to make ends meet, or are having a hard time finding work because you lack experience, the cover letter is not the place to mention this. In fact, this isn't something to say to anyone hiring or anyone you work for. This is something to say to your friends.
The websites applicants provided gave me a glimpse of their personalities, writing skills, & organization.
Out of about 40 applicants, two applicants went a step further and provided a list of what skills they brought to the table in relation to the job requirements. Excellent.
For more tips I highly recommend this best of Craigslist article: Tips for applying to a job from Craigslist. You'll find spending a little more time customizing and polishing cover letters is worth it.