When troubleshooting portal performance issues, it would be helpful to have a report of average portlet render times so you can more easily get an idea of whether portlets are taking a long time rendering and slowing down the overall portal response time.
You can often gather this information on a live system by noticing a single page/tab tends to be slow compared to the rest of the system and minimizing the portlets on the page to figure out what is going on. It would be helpful to have a report to look at historic data.
There is already a PortletRenderExecutionEvent event created that has the render execution time. What's missing is an aggregator to process the data (I believe there is one to count executions, but does not do anything with execution time) and having a statistics report on it.
Another interesting idea is to put something in the page markup for each portlet that indicates the portlet's execution time that could be incorporated into Google Analytics reporting. I'm not very familiar with the Google Analytics reports, but if there is a way to look for data attributes on the portlet chrome divs that contain the render times in a way that GA could produce reports on it, I think that would be a cool alternative to having the reports only in the portal statistics.