[eschwartz]

Just make sure Dropbox only knows of one calibre library, and that it is the one you want. That is what really matters and as long as you do this, it will work as you expect.

And let me take this opportunity to provide a general Dropbox+calibre warning: Do not, under any circumstances, open a calibre library on two synced computers at the same time. Always make sure the library has been completely synced, before AND after you use calibre on either computer, and then stop Dropbox while calibre is open!

You do not want to accidentally edit the same books twice and end up with two conflicting copies, neither of which calibre knows about. Make sure all your edits are saved in Dropbox before editing on another computer. (And yes, even opening calibre will edit the database itself.)

(I'm not saying you don't know this already, but better safe than sorry, and many people make this mistake.)