I started using BibDesk (http://bibdesk.sourceforge.net/ http://bibdesk.sourceforge.net/) with Dropbox just last week and have been pretty happy with it so far.

I started using BibDesk (http://bibdesk.sourceforge.net/ http://bibdesk.sourceforge.net/) with Dropbox just last week and have been pretty happy with it so far. I don't have anything, yet, for books, but I suppose I could just write BibTex entries for the books and be done with it.