Lost Dropbox context menu entries, file and folder status indicators in Finder after updating to Yosemite
It turns out Dropbox' self-updating wasn't functioning. The program was several versions behind current.

I was able to restore Finder context menus and sync status by going to the Dropbox download page, downloading and re-installing Dropbox. After getting version 2.10.41 the sync status indicators and context menus were returned to the main Finder windows when browsing under my Dropbox folder.

I did not have to uninstall or even stop the currently-running Dropbox service instance. The installer took care of all of that.

The latest Dropbox version that run properly with Yosemite is 2.11. Go to : https://forums.dropbox.com/topic.php?id=121399 and click on "offline installer" link for Mac OS X. Don't forget to restart your Mac after installation.