6 Questions about Submitting to Literary Magazines

I have some questions for you all in regards to submitting short stories, poetry, creative non-fiction, etc. to literary magazines:

-How do you keep track of what you've submitted where and when?
-How do you find new magazines to submit to?
-How do you tell which magazines tend towards your type of work? [something more efficient though perhaps less effective than the obvious answer of reading the magazine.]
-What do you put in the cover letter when they ask you to write a cover letter.
-How do you know when a piece is ready to submit?
-How do you know when to give up on a piece, and what do you do with it then?

I have some answers to these questions, but they either aren't working for me as well as I would like, or I would just like some corroboration or fresh ideas. I keep track of pieces by listing them in a word document along with where and when I've submitted them, color coded with submitted, accepted and rejected. I look on Duotrope.com and NewPages. I am very lacking in ideas for how to see which magazines would like my work. I usually put previous publications and maybe something interesting about myself in the cover letters. I never think a piece is ready to submit, but I submit it anyway, and I'm still thinking of what to do with pieces I've given up on, but one place I've been using lately is DeviantArt. I've heard that a good rule of thumb is forty rejections.

Anyway, I really would love your answers to any or all of these questions. Any advice could make my and other writers lives much easier. So, what are your brilliant or even not-quite-brilliant ideas?

Sarah Allen