automatic clear the clipboard after some time

Thanks for this suggestion. As the new Diodon version (currently available as test version) is storing its items infinitely it would certainly makes sense to delete items which are older than a given time.

This might not necessarily be implemented in Diodon itself but could also potentially be available in the System Settings Zeitgeist Privacy module.

For now as a workaround the Privacy module can be used to clear items older than a given time (see here http://esite.ch/2013/12/29/storing-clipboard-items-infinitely-test-version/ )

Added issue concerning such a feature in Zeitgeist here https://bugs.launchpad.net/activity-log-manager/+bug/1305545

I agree - and indeed even asked a Launchpad question about this, before I saw this bug report. Is there a command to clear the data (a command I could get my system to run on e.g. logout)? If there is, does the command clear everything Zeitgeist stores?

As mentioned in the question you can set `ZEITGEIST_DATABASE_PATH` to `:memory:`.

Depending on your desktop environment something like:
echo "ZEITGEIST_DATABASE_PATH=:memory:" >> ~/.pam_environment

It would still be great to have a more convenient setting for this.