Is it possible to purchase books and send directly to calibre?  I have a Sony reader that already has a good number of books but might like to add more without having to reinstall the

Sony Reader software if possible.  

I have a Sony reader and I've never installed the Sony software.  Just install Calibre.  Download your ebooks into a folder on your computer, open Calibre, and click "Add Books".  Navigate to the folder where you have your ebooks stored, click on the one you want, and then "open" and it'll import into Calibre.  Then, hook your reader up via the USB cord and Calibre will detect it.  Just click "send to device" and they'll go right onto your Sony.

After a bit of monkeying, I got the books on my Sony to all show up in Calibre, and downloaded a few new ones from there to Sony.  Thanks Sarah!