kovidgoyal,
Just want to mention how much I love calibre. I have been looking for something like it for years. Found it about 6 months ago and it has made my digital life much much easier. Now my ideal would be for your calibre to integrate with readerware which I use for my physical library.
I suppose I could figure out how to import my readerware library as blank entries into calibre. I like readerware though because it allows me to use a barcode scanner on my books in bulk to import them as well as I have the network version and access it remotely from client computers. I have about 5000 books in that database and another 5000 or 6000 to go before it is fully populated. The hard part with that one is where to put 10 or 11 thousand physical books.
This reminds me.. I donated a few dollars after I started using calibre but I like to support products I use that are open source and as actively developed as yours is so I just kicked another few dollars your way
I love it.
I hope that a lot of the other people that use it donate some here and there also.