That and Calibre wants to automatically organize all my readable files for me in a space-consuming database of its own, I installed it several months ago to translate some old books in a defunct reader format into ePub. Two hours into the first conversion it was still grinding away. I finally had to drag it out back and shoot it 18 hours later with a 'kill -9', then cleaned up the file system by hand. It had converted one novel in that time, and was only on the second. Probably because its database-building (with full copies of each book in the database) was hammering the filesystem.
I ended up using an online tool for that conversion, file by file, about 3 minutes per file. Tedious to feed it by hand, but I got my books converted.