Liferay has an audit framework that would be appropriate for this,
you just have to find the right places to inject the audit message
creation and posting.
It's hard to know from a portlet perspective what a user may
or may not have seen. I mean, you can tell that they visited a page,
but that's it. You won't know if they actually looked at the portlet
or scrolled the page to bring it into view or anything specific like that.
You could leverage portlet filters if you needed to get to a
per-portlet-interaction kind of level...
