I've used the 12.04 live cd to get here but installed it awhile ago. I assume until a week ago I was current but now I'm not so sure. Maybe I'm just being paranoid?
Let me explain the way how package updating & upgrading works. Also, I'd like to cover distinguishes between them.
So, returning to your question, the 'updated x hours ago' message means that your package lists are updated, and there are not updates for installed packages. This is typical for LTS releases which are not frequently updated releases. They [almost] rarely receive security and stability updates. And for accomplishing the same thing that the GUI update manager does you should run in the terminal: