I've recently done a huge import of fic to Calibre - I've been using Pocket (used to be ReadItLater) to read fic on my iPad, so all I had to do was click a button in my brower and the story showed up in the app.

For backup purposes, I exported the over 10.000 links I had saved, and found that I can import several thousand links into Calibre at once - you can paste a looong list of links into the import field.