I'm very happy that the GPL issues with TomTom have now all been settled, and despite some early disagreements we're now very happy with the way TomTom has handled this case.
The TomTom GPL page contains the latest source of their 4.42 firmware. Pretty much all of the drivers have been released with their source code (touch-screen, framebuffer, USB device, accelerometer, GPS). Only (obviously) the SD-Card driver is missing in the source and provided as kernel module. This is due to the stupid SD Card Alliance licensing agreement, which basically puts every recipient of the Documentation under an NDA.
So at the moment you have to put all of the OS into the initrd, which is loaded by the bootloader.
We're working on a solution for the card reader, though. At least MMC Card support should be available soon.