Calibre is an unbelievable product. As soon as my wife finds another job I'm definitely donating. I can't believe how power this application is.
I've only been using the software for a couple days and I'm struggling to find anything that I don't like or that is missing. However, there is one thing I thing that would be useful and probably quite easy to implement... Web Searching.
It would be nice if you could right click on any Title and in the context menu have an option for Web Searching. In there you could have options like Search Author of Wikipedia, Search Author on Amazon, Search Author on Google Books, Search Title on Amazon, Search Title on Google Books.
Even better, allow you to have some control of what search sites shows up in the context by toggling them in the Preferences. That way if search sites are created that people don't care about they will not be visible.
Just an idea. Take it for what it's worth. Not everyone will agree, that's fine. I just find myself going to these sites regularly when playing in my database.
Keep up the GREAT work!