Check the configuration of your Tag Cloud widget, as by default it only shows Tags that are used by at least 5 posts.
Go to Graffiti Admin > Presentation > Widgets and click "edit" on the tags widget. Look at the setting called "Minimum Number of Posts" and change it to "no minimum" if you want ALL tags to show up even if they are not
used by any posts. Or you could choose one of the minimum # of post levels.
We should probably change the default value it's not so confusing. :)
Hope that helps!