You need to whitelist programs to have them show their notification / tray icon in unity.
To see what’s in the whitelist:
gsettings get com.canonical.Unity.Panel systray-whitelist
This will result in something like this output:
['JavaEmbeddedFrame', 'Mumble', 'Wine', 'Skype', 'hp-systray', 'scp-dbus-service']
To have Wuala and Dropbox icons appear you’ll need to set the array to:
gsettings set com.canonical.Unity.Panel systray-whitelist "['JavaEmbeddedFrame', 'Mumble', 'Wine', 'Skype', 'hp-systray', 'scp-dbus-service', 'Wuala', 'Dropbox']"
Or to allow all panel icons:
gsettings set com.canonical.Unity.Panel systray-whitelist "['all']"