Whenever I watch videos, either online of local via Totem and/or open PDF files using evince.

The system gets really, really bogged down. All apps get really slow, menus take forever to display, switching windows gives me time to make a coffee, etc.

I have a couple of bug reports open on this, but what do I need to do to really troubleshoot the issue?

I've purged Adobe Flash from the system, but YouTube HTML5 videos still have the issue. A bunch of PDFs saved locally trigger the problem.

And to (temporarily) remove the slowness, I need to shutdown the computer, breath for a few minutes, then restart. A simple reboot does not do the trick.

How can I identify the cause?

This only started on 13.04. I've had Ubuntu on this machine for a year without a problem until "upgrading" to 13.04. I am not a programmer, but I suspect an issue with the Intel video driver.