Dropbox is for people that can't use rsync+git. For the unix-competent, it's not particularly difficult and we managed for many years with the previous tools, rsync+svn or even rsync+cvs
The way I look at it, I've got limited time. I can spend it fucking around duplicating infrastructure, or I can spend it on something that matters more to me.
I'm among those who don't see any need for Dropbox, but readily admit that obviously millions of others do.
They do not do what dropbox does.