I use Papers with Dropbox for syncing my library. Works pretty well as long as you don't try to run it from several computers simultaneously. I'm pretty happy

I use Papers with Dropbox for syncing my library. Works pretty well as long as you don't try to run it from several computers simultaneously. I'm pretty happy with Papers, too, though I must second the other post about the Mac app being related to second class status. There has been basically no feature improvements (highlighting, for crying out loud) since 2008 when I started using it. Now I use Skim for annotating instead, which is a bit lame since you can't see the annotations within Papers, but the advantages outweigh the disadvantages.