We don't read them usually, unless it's for something like a technical writing position. We're really looking at skills, and since we do so much international work, all a cover letter does is point out potential language barriers. We're interested in getting around those kinds of barriers. I think another common mistake is that new graduates are so focused on what they are looking for, they don't ask the employer what it is looking for in a candidate. Part of this is the result of the aggressive hiring that good companies do at colleges.
Students realize they are a commodity.
However, good manners still separate top candidates from less desirable ones. We track all our responses and identify how many come from which sources, but the key is not to get too tied up in one program for the wrong reasons. An example would be participation in traditional job fairs. It might seem like all the other companies are going, and they may be good PR tactics, but you have to look at your cost per hire. If you're not making any hires from the event, maybe you need to look at other, more productive avenues.