[mindcrime]

They totally do! And epub, mobi, djvu...

    prhodes@troubadour:~/Downloads/pdfs$ find . -name "*.pdf" | wc -l
    18952
    prhodes@troubadour:~/Downloads/pdfs$ find . -name "*.epub" | wc -l
    2385
    prhodes@troubadour:~/Downloads/pdfs$ find . -name "*.djvu" | wc -l
    1384
    prhodes@troubadour:~/Downloads/pdfs$ find . -name "*.mobi" | wc -l
    125

(There are definitely duplicates in those, FWIW)

[NoMoreNicksLeft]

Why are you downloading mobi files? Seriously, I only do that if there is no epub, and only keep it long enough to convert it.

[mindcrime]

Pretty much that. If the only copy I can find is .mobi.. or, occasionally perhaps, just by mistake.