Firstly, I would like to say how much I love your program. It has really enhanced my enjoyment of my 505.
Anyway, two things that irk me slightly.
1) When I click 'remove book' from the main library page, it should ask me if I simply want it removed from Calibre, or to be deleted from my PC. As it stands, I can't click this button without going to fish the files out of my recycle bin.
2) When clicking 'send to device' it should pay attention to what your preferred file format is. So it should either a) send that format as default or b) that file format should be top of the list. I just think this button should have a "one click" feel to it.