I reinstalled Ubuntu desktop using the minimal CD image and the following command:
$ sudo apt-get install ubuntu-desktop --no-install-recommends
After that I used Ubuntu Software Center to make sure Unity supports application indicators: http://i.imgur.com/bYF162w.png.
Everything works great, except for Dropbox. For some reason the icon doesn't appear in the tray, even though the application is running. Steam on the other hand runs just fine, so it seems like there is nothing wrong with the tray itself.
According to this post the tray icons should be in
/usr/shared/icons/hicolor/22x22/status but it doesn't contain any Dropbox icons. Neither do any of the other resolutions. The answer is a bit outdated, so I'm not entirely sure it is still applicable to the current version of Dropbox.
I did the usual thing of reinstalling dropbox with:
sudo apt-get purge nautilus-dropbox sudo apt-get install nautilus-dropbox
But that didn't solve anything either.
Does somebody know how to fix this issue?