Dropbox integration in Linux Mint KDE is problematic out of the box. The default dropbox package integrates with Nautilus, the Gnome file manager.

There's a tutorial for manually installing Dropbox in KDE: http://www.nixternal.com/kde-and-dropbox/

I don't recommend doing that. After some digging and experimentation, I finally found a PPA for kfilebox: ppa:blue-shell/kfilebox

Launch Konsole to get a command-line session. Enter the following commands:

sudo apt-add-repository ppa:blue-shell/kfilebox
sudo apt-get update
sudo apt-get install kfilebox

I'm still testing this set-up and may need to add to this tutorial. But, right now Dropbox is installed and working.

Cheers.