It bears redundant repeating again
Proofread your cover letters. Set them aside for a week to gain fresh eyes. Hand them to six friends to proof. Read them sentence-by-sentence from the end to the front. Read them out loud.
I just received a lovely letter from a job seeker that didn't pass muster. The person was not applying to a particular job, but rather sending out their resume following the oft-repeated suggestion that it's good to ask the place where you want to work if they happen to have any jobs available, either now or coming up. Bravo for initiative! However, this makes it doubly tragic, as there was no reason the applicant couldn't have spent a little more time checking.
I'm a picky bastard when it comes to errors in writing, and I can hardly claim to be perfect. HOWEVER, there's a big difference between a cover letter for a job as an editor, and just about any other sort of writing (except perhaps a column about writing mistakes. Alas, I'm sure something has crept in here).
Anyway... In the second paragraph--the "meat" paragraph, if you will--of this letter, the writer commits several errors. They're multivaried and subtle errors, but the sheer accumulation does not speak well. Among them:
1. misplaced comma (though a subtle misuse, so only half a point off)
2. misused word (it almost is the right word, but the connotation is wrong)
3. omitted hyphens (though not in a hard-and-fast rule, so no points off)
4. omitted word
5. poor parallelism, creating a clunky sentence
6. misspelling, confusing a word with a homophone
That's all in one paragraph. It appears to be the worst paragraph (I'm no longer reading closely), but the rest of the letter has overlong sentences and some stylistic stilting that is forgivable, but failing to impress.
Fortunately, this applicant appears to be looking for a position in manuscript editing, not copy editing.
Overall, the writing was a thousand times better than most people could do, and significantly better than most of the applicants' letters I've seen in my day. I daresay other readers wouldn't have spotted errors 1 and 3, and only a few would have picked up 2, 4, 5, and 6. Alas, for copy editing, the picayune is important.
On the plus side, the applicant knows what a semicolon is and the proper way to use it.