Forcing Zeitgeist to index Dropbox folder

Actually the Dash in 12.04 is also hooked up to "locate". If your Dropbox folder is in your home folder it should eventually be indexed by locate. If you don't want to wait for this to happen automatically (I don't know how long that would take) you can just run "updatedb" in a terminal to force indexing. Note that typically the locate database is owned by root, so you need to run sudo updatedb. Now even files not covered by zeitgeist should show in the Dash.

Source

Zeitgeist is not an indexing service. For Dropbox transfers to appear inside Zeitgeist, the Dropbox client itself would have to tell Zeitgeist about the events. If you want all the files under there to appear in the dash search, you'll have to open them all, probably from the file manager, so that they get added to the Zeitgeist log.