Originally Posted by Iņigo
Some years ago I used to use a free ext2 driver for my work Windows XP laptop...
Ok, it's still there: http://www.fs-driver.org/
Maybe it can be useful for you.
EDIT: note it looks like Windows 7 is not supported currently
I am a linux user myself and do not use windows if I can avoid it. For me the reformatting to ext2 is not a problem at all. Calibre recognizes and mounts the device just fine. A manual mount also works if I want to copy non calibre content.
Your tip sounds like it might be work for windows users. I have no idea if calibre on windows will automount.