How can I visualize progress in a panel? &nbsp;&nbsp;I want to put a list with progression bars into a panel or somewhere else. Is it possible to place a custom image next to text? Or draw progress bars like the one in the header somewhere else?

I found this line in space_info.py:    layout.template_running_jobs()
but I'm not clear about how to find the corresponding code.

&nbsp;&nbsp;My workarounds would be to use a crude text version of a progress bar or a slider. But my ideal thing would be a bar with colors of my own choosing.
No you can't (not without fairly bad hacks at least).

As of 2.69 this is a limitation in the Python API, layout.template_running_jobs() shows progress for blenders job system which Python has no access to.

You can however control the mouse cursor to display progress.