I haven't had formal qualifications for any of the few jobs I have been hired to do in the past 6–7 years, and my cover letters were almost always the reason I got an interview. I would like to think that my cover letters are not the standard, boring ones -- and I purposefully honest with a bit of humour.

In contrast, the accompanying resumes have been single-page, no-frills resumes -- I don't even bother saying anything about what I have done/achieved in previous roles because it seems pretty pointless when I don't have any certificates or practical experience to show.

I'm sure it's different from industry to industry, from company to company, and depends on the seniority of the role. It's just what worked for me to get interviewed at small-medium businesses and probably doesn't work for everyone.

As a final note, in some way I also treat the way I prepare my cover letters and resumes as an additional indicator for whether or not I really want to work at a company (particularly smaller ones with no HR departments): if they don't get back to me it's most likely that they are only looking for "the piece of paper" and/or they don't like my personality/the way I communicate.

Edit: typos.