I've Recently downloaded calibre and with it up and running on my Ubuntu Linux machine started organizing my collection of about 1800 e-books in various formats. I'm very impressed with it's capabilities.
In the past I developed and used a library inventory/book checkout program that was based on a MS Access database for over 10,000 volumes with custom-coded electronic forms for data entry, so believe me when I say I like calibre very much. The learning curve isn't too steep, and it has features that we were only considering adding - for example, looking up metadata on-line, rather than reading the copyright page and typing it all in. That's a very big deal for me.
In fact, I have recommended calibre to my daughter for organizing her e-book collection as well. If you ever decide to branch out into DVD organization, I'll tell my sister too.
Great work, keep it up!
Bob63