Look at how volume and brightness control is done on a Macbook. They took function keys and repurposed them into crude up and down buttons. To get fine control you have to hold down the Shift and Alt keys. If you want to actually use the "function" part of the function key, you have to hold down the Fn button.
A touch control there could present a more intuitive interface--tap the control you want, then use a touch slider to adjust with great precision.
Another idea I saw in a blog post was to put a scrubber control there during video editing. Currently the trackpad has to serve double duty controlling the features of the application, and controlling the scrubbing of the content.
The function keys are a UI mess. Each serves double or triple duty, and the duties sometimes change with OS releases. For example, the Dashboard key on my Macbook Pro no longer activates the Dashboard.
This is just like the situation on smart phones when they all shipped with physical keyboards. Each tiny button on my Blackberry had at least 2 different functions. As Steve Jobs said, "we solved this problem with a bitmapped screen and a pointing device."
