Nemo, the default Cinnamon file manager, needs Cinnamon to be installed, even if you want to use it in some other desktop environment such as GNOME/Unity. That’s not the only issue that makes using the latest Nemo under Unity difficult – Cinnamon 2.0 breaks Unity in Ubuntu 13.10, Nemo no longer draws the desktop icons and so on.

Update: the PPA now provides Nemo 2.8.7 for Ubuntu 16.04, 15.10, 15.04 and 14.04.