Just installed 16.04. Previously with same hardware Dropbox was working. Reinstalled OS due to a hard drive crash, and installed Dropbox. Dropbox icon appears, but can't be used as menus don't appear. This is a well-known issue that's been around since 14.04 at least.
There is a fix that is mentioned several places such as here
dropbox stop dbus-launch ~/.dropbox-dist/dropboxd start -i
That will theoretically start dropbox with the system tray ("notification area") icon, instead of the nonfunctional "indicator area" icon.
When I try using dbus-launch, I get this error message:
$ dbus-launch dropbox start -i Unable to create /home/~/.dbus/session-bus
Googling and digging into that error sent me down a rabbithole to a lot of stuff I don't understand. For example reading man pages on dbus-launch and not understanding a single sentence of it. I think it's above my pay grade. I also tried launching the command dbus-launch dropbox start -i as SU but that gave the same error. I understand that launching dropbox as sudo will not work long term, I was just grabbing at straws.
I can use the dropbox command-line interface, however it does not allow me to log onto my account, set up a different folder for dropbox, and so on.
How would I go about achieving use of the Dropbox GUI interface and work around this error?
[Edit] Also attempted using
dropbox stop && DBUS_SESSION_BUS_ADDRESS="" dropbox start
this did not produce an error message, however the icon dropdown menu remains nonfunctional and the dbus-launch method still produces the same error message.
 for no apparent reason, this icon seems to be working now despite the error. See my answer to my own question below.